General features and proportions

Table 2 summarizes the measurements and body proportions of the specimens described here as Paraclupea seilacheri sp. nov. The overall body shape of this species resembles that of other double armored herrings, as Paraclupea chetungensis^{Sun, 1956}, and Ellimmichthys goodi (^{Eastman, 1912}) (see ^{Chang and Grande, 1997, figs. 3, 7}). In lateral view, P. seilacheri is a dumpy looking fish with a rounded abdominal border, in which the maximum standard length (SL) known is 118.8 mm and corresponds to specimen IGM 4721, whose total length exceeds 154.4 mm. In this species, the maximum body depth and the head length represent 50.9 and 32.9 % of the SL, respectively. The maximum depth of the trunk is present just before the half body length, in the point where the dorsal fin arises (= predorsal length) and the dorsal body profile forms an obtuse angle, at 49.3% the SL. The depths of the head and caudal peduncle are about two thirds and one third of maximum body depth, respectively. The head is triangular; slightly longer than deep.

In this new species, the caudal fin is almost as depth as the trunk. Both caudal lobes are triangular and deeply forked. Unpaired fins are triangular, relatively smaller, and not opposed to each other. On the back, the dorsal fin represents about 18.6 % of the SL, and it is located along the 49.3 and 67.9 % of the SL. In contrast, the anal fin occupies about 18.9% of the SL on the ventral body edge, and it is located at the beginning of the posterior half of the body, along the 77.9 and 96.2 % of the SL.

The paired fins of Paraclupea seilacheri sp. nov. are relatively short. The pectoral fin is located behind the pectoral girdle, slightly below the midpoint between the vertebral column and ventral body edge. The larger pectoral rays cover the anterior half of the distance between the bases of the pectoral and pelvic fins. The pelvic fin is placed below the posterior half of the dorsal fin at 57.5 % of the SL; its larger rays are two thirds of the larger pectoral rays.

Skull

The head is laterally preserved in all specimens of Paraclupea seilacheri sp. nov. studied here (Figures 3 - 5). The head is triangular, about 1.5 times longer than deep; its otico-occipital, ocular, and ethmoid sections are about of the same length.

The frontals roof large part of the skull; they are flat and roughly triangular, narrow anteriorly and broaden posteriorly (Figure 5). In their posterior portion, these bones suture with the parietals, pterotic and autosphenotic. Frontals are joined together throughout their length and there is no fontanelle between them. Frontals are smooth bones except for a small posterior area, near the parietals, where they are strongly ornamented with irregular ridges. The supraorbital sensory canal runs along the frontals enclosed by bone.

Parietals are small sub-square bones that meet each other along the middle line of the skull and separate the supraoccipital and posterior end of frontal bones. There is no temporal foramen. Parietals are strongly ornamented with fine ankylosed sigmoid ridges forming a reticular pattern. The supratemporal commissure runs, enclosed by bone, along side the posterior edge of the parietals. The supraoccipital is a small bone in the posterior margin of the skull that carries part of the supratemporal commissure; it is restricted to the tip of a stout supraoccipital crest (Figures 5, 6). Beyond the parietal, the posterolateral end of the supratemporal canal communicates with the extrascapular canal.

The pterotic is a rectangular bone in the lateral skull wall; it meets the parietal and frontal medially, the epiotic and epioccipital posteriorly, and the large triangular dermosphenotic anteriorly (Figure 5). A small thin pre-epiotic fossa is present between the pterotic and epiotic. There is no evidence of the recessus lateralis on lateral skull bones. The hyomandibular fossa is roofed by the pterotic and dermosphenotic bones (Figure 5). The epioccipital is short, massive and restricted to dorsoposterior part of the skull. Bones in the lateroposterior and otic skull areas are obscured.

The orbital section of the parasphenoid is an edentulous rod like ossification; at the end of the orbit, it carries a small basipterygoid process that is projected anteroventrally (Figure 5). In IGM 4721, the postorbital part of the parasphenoid is partially exposed (Figure 6); here, this bone is extended along the entire ventral skull edge. Above, the prootic is exposed showing a medial irregular surface with appearance of strawberry that here is interpreted as a superficial expression of the bulla as previously interpreted in other fossil clupeomorphs by ^{Forey (1975)} and ^{Grande (1985, p. 253)}. This specimen also shows the triple joint surface on the anterior face of the first vertebral centrum, which includes a large ventral surface to joint with the basioccipital and two small dorsal surfaces to joint the couple of intercalar bones. The first vertebral centrum also reveals a dorsal surface to joint with the respective halves of the neural arch.

The mesethmoid is a massive bone with a rounded massive edge and a flat rear overlapped by the frontals. On each side, this bone shows a lateral process ending in a facet for the respective palatine head. The lateral ethmoid is a thin roughly rectangular bone that encloses the posterior ends of the nasal capsule, and is located between the frontal and parasphenoid. The nasal is a small and posteriorly tapered tubular bone placed over the ethmoid area. Only small parts of the pterosphenoid and orbitosphenoid bones are exposed in some specimens studied here (Figures 5, 6).

Upper jaw

Upper jaw consists of the premaxilla, maxilla and two supramaxillae. The premaxilla is a sickle-shaped toothless bone, about one-fourth the maxillar length. The maxilla has two sections forming an obtuse angle. The anterior toothless maxilla section is a smooth and rod-like structure tilted upward; in contrast, the toothed maxilla section is a flat, almost straight, and horizontally lamina, slightly longer than the last, in which the external surface is ornamented with scarce reticular grooves. A single row of small, uniformly spaced and sized, conical teeth is present along the ventral edge of the last maxillar section. Two drop-shaped supramaxillae are present overlapping the dorsal edge of the toothed maxillar section; the anterior is slightly smaller and rounded than the posterior one that has a long and sharp dorsal process. External surfaces of supramaxillae also are ornamented with scarce reticular shallow grooves (Figures 5, 7).

Lower jaw

This jaw consists of dentary, anguloarticular, and retroarticular bones. The lower jaw shows a shallow and short ventral postarticular process. The dentary is triangular with a shallow symphysis, a high coronoid process, and a sinuous alveolar border relative short and tilted upward. A row of small conical teeth is present along the alveolar border of this bone; the shape, size, and distribution of these teeth resemble those of the maxilla (Figures 5, 7).

The anguloarticular occupies about two thirds of the lower jaw length; it forms the bulk of the postarticular process and the articular facet for the quadrate. The small retroarticular bone occupies the ventral end of the postarticular process. The mandibular sensory canal runs alongside the ventral border of lower jaw; this sensory canal opens in six or seven pores that are present from the postarticular process to dentary symphysis (Figure 5).

Circumorbital bones

These bones are flimsy and flat. Since these are strongly fractured in all the specimens studied; their number and shapes are only partially known. The circumorbital series includes the antorbital, dermosphenotic, and probably four infraorbitals. Among these bones, the first four infraorbitals are located below the orbit covering part of the ectopterygoid and endopterygoid. The infraorbital sensory canal runs near the dorsal edge of the infraorbital bones (Figure 5).

Suspensorium

The hyomandibular is a hatchet-like bone with a single stout head and a narrow long shaft ventrally projected. This bone shows a well developed opercular process located at the base of the back of its head. The quadrate bone is triangular; its articular condyle is inclined forward and lies beneath the anterior half of the orbit. The spiny posterior process of the quadrate is as high as this bone. The symplectic is about twice longer than the posterior process of the quadrate (Figures 5, 6).

The metapterygoid is a roughly square bone that bears numerous rounded and regular sized teeth on the anterior a middle part of the lingual surface. The ectopterygoid is a smooth, narrow, and curved bone, in which the vertical and horizontal limbs form an angle a little greater than 90°. The ectopterygoid meets the ventral border of the endopterygoid and the anterior border of the quadrate. The endopterygoid is a long and semi-ovoid flat bone, wider than the ectopterygoid; its entire lingual surface bears numerous rounded and regular sized teeth, like those that cover part of the metapterygoid. The palatine is as long bone with a small stout head that dorsally articulates with the lateral process of the mesethmoid and ventrally with the maxillar palatine facet.

Opercular bones

The preopercle shows an inverted L shape, in which the length of the horizontal anterior limb is about one half the height of its vertical dorsal limb. The preopercular sensory canal runs close to the inner edges of this bone, it presents three to four branches on the horizontal limb and only one in the vertical limb (Figure 5).

The opercle is a kidney-shaped flat bone, higher than long, with the anterior edge straight and thick. Its surface is covered with fine straight parallel grooves that radiate from the area of its hyomandibular facet. The subopercle is a semicircular bone with a straight dorsal border, a gently curved ventral edge, and a small upward spiny anterior process. The interopercle, located below the preopercular horizontal limb, is a smooth, flat, and spathiform bone (Figure 5).

Branchiostegal rays and branchial arch

Bones of the branchial arch are partially or totally covered in the specimens studied (Figures 5, 8). The anterior ceratohyal is rectangular, about twice longer than high; this bone is pierced by a large beryciform foramen and has a horizontal groove for the afferent hyoidean artery. The center of the semicircular posterior ceratohyal is also pierced by a small foramen. In front of the anterior ceratohyal, the dorsal and ventral hypohyals have similar size and are strongly attached to each other. There are 10 flat and blade-like branchiostegal rays that progressively are longer and wider. In IGM 4722, the urohyal is elongated and has a small anterior head.

Axial skeleton

In this species, the vertebral column is composed of 38 to 39 centra, including 20 to 22 abdominal, 16 to 18 preural, and 2 ural (Figures 3, 9; Table 2). In the preural region, the vertebral centra are rectangular, slightly higher than long, sculpted with longitudinal ridges and pits. The complete and well articulated specimens studied here seem to have the centra fused with the respective neural and haemal arches; however, IGM 4718, where some centra are disarticulated and scattered, reveals that at least the most anterior abdominal centra are not fused with the neural arches. In the most anterior abdominal centra the apex of the neural spines is bifid. There are 20 pairs of long curved ribs that almost embrace the entire abdominal cavity. The heads of the most anterior ribs are stout and joint with the cavities in the ventrolateral surface of the respective abdominal centra. The last twelve abdominal centra show straight and downward parapophyses; these tend to be longer in the posterior vertebrae. The proximal ends of posterior ribs joint with these parapophyses except the last three, which are floating ribs that do not reach the parapophyses.

Long epineurals are associated with the abdominal centra and the anterior half of preural centra. In the anterior abdominal centra, the epineurals are three centra long, thin, and curved bones, projected laterally upward and backward from the bases of the neural arches. Beyond, these bones are progressively shorter and located on the neural spines, away of the neural arches. In addition, in the preural centra each epineural develops a thin anterior ascending process that gives the Y-shape to this bone.

There are seven epipleurals, thin and slightly curved, associated with the last nine abdominal and first three or four preural centra. These bones rest horizontally below the centra and almost have the length of two of them. In the abdominal area, the epipleurals meet the parapophyses and ribs while those of the preural area do this with the haemal spines.

There are seven predorsal bones (named as supraneurals by ^{Forey (1973)}) between the occiput and the dorsal fin base, below the predorsal scute series. These stick-like bones increase in size in anteroposterior order, show ventral tips slightly curved forward, and have small anterior and posterior laminar wings or expansions.

Pectoral girdle and fins

In the top of the pectoral girdle, the posttemporal is a flat, ovoid, long bone with the dorsal process hypertrophied, rectangular and wide; the surface of this bone is excavated by numerous branches of the posttemporal sensory canal. Below, the supracleithrum is a flat an ovoid bone that is slightly curved and long; the cleithrum is S-shaped with the posterior vertical limb being slightly higher than the anterior vertical limb. The pectoral fin is located below the corner between the middle horizontal section and the posterior vertical limb of the cleithrum. Two long, ovate, and flat postcleithra are present behind the posterior vertical limb of the cleithrum. Other bones of the pelvic girdle are obscured in all the specimens studied here (Figure 5).

The pectoral fin consists of 16 branched and segmented rays. The longest of these rays equals the length of six abdominal centra. Although it is difficult to recognize the endochondral elements of this girdle, at least four proximal radials articulate with the pectoral fin rays.

Pelvic girdle and fins

The pelvic fin is triangular, short, and opposed to the posterior half of the dorsal fin. This fin is located just at the beginning of the posterior half of the body, at 58 %of the SL, beneath abdominal centrum 19. At least six pelvic fin rays are present in this species, problably these are a few more because the smaller rays are generally covered in all the specimens studied here. The length of the larger pelvic rays equals the length of three abdominal vertebrae. The pelvic bones are unknown because the abdominal scutes cover them (Figures 3, 4).

Dorsal fin

This triangular fin is short and rises just at the end of the first half of the SL. The length of the dorsal fin base represents 19 % of the SL and is extended above the last ten abdominal vertebrae (12 to 22). This fin consists of two small unsegmented and unbranched rays and 17 branched and segmented rays. The fourth branched ray is the longest in this fin; front and behind it other rays are progresively shorter (Figure 9).

There is a series of 16 proximal pterygiophores supporting the dorsal fin rays; these are rod-like elongate structures with anterior and posterior laminar expansions or wings. The first of these elements is the longest and the only bifurcated in the series and joints with the first two small, unbranched, and unsegmented dorsal fin rays (Figure 9). The posterior proximal pterygiophores become progressively shorter and each of them joints only one ray. Some middle pterygiophores are present between the dorsal heads of the proximal pterygiophores; these are stout rectangular bones. Small rounded distal pterygiophores are also present but it is hard to determine if these are present along the entire series. At end of this fin, there is a small and expanded dorsal fin stay in horizontal position.

Anal fin

The anal fin is short and located far at the back of the trunk, behind the dorsal fin level (Figures 3, 4). The anal fin length is about 17 % of the SL; it rises in the last fifth of the body (at 78 % the SL), below the preural centra 4 to 11. Unfortunately, the rays of this fin are not well preserved in any of the referred specimens. Although the anal rays are unknown; these could be one or two units more than those 16 pterygiophores or proximal radials that internally support this fin. These internal rod-like structures are slightly curved and of decreasing sizes. The distal ends of the pterygiophores almost reach the tip of the nearby haemal spines. Small distal and middle pterygiophores or radials are identifiable in the base of the anal fin.

Caudal fin

The haemal and neural spines of the last four preural and two autogenous ural centra support the elements of dorsal and ventral caudal fin lobes. The neural and haemal spines of the three posterior preural centra are wider than the anterior ones (Figure 10). The caudal fin is deeply forked. The rays that constitute the dorsal and ventral caudal fin lobes are one unbranched, 10 principals, and 6 procurrents, as well as one unbranched, 9 principals, and 7 procurrents, respectively; additionally, there are two and one caudal scutes preceeding these caudal lobes in the same order. The anterior ends of all principal rays are pointed but in the two most internal caudal principal rays, in which ends are expanded and bifurcated.

The stout parhypural and the preural centrum 1 are fused. The first preural centra and ural 1 are of the same size while the ural 2 is smaller. It seems that an expanded neural arch is present in both ural centra. On the first preural centrum, the neural arch and its respective spine form a broad leaf-like structure, so expanded that it fills the space between the spine of the preural 2, the neural arches of both urals, and the epurals. The hypural 1 is an autogenous fan shaped or triangular structure that joints with ural 1. Above hypural 1, six spathiform hypurals are present, placed side by side; all of them joint the ural 2 and seem to be autogenous too but the hypural 2 that is fused with ural 1. There is no a caudal diatema (= hiatus or free space) between the hypurals 2 and 3.

There are three wide epurals located behind the spine of preural 1. There is no evidence of urodermals. There is a series of three uroneurals. Uroneural 1 is a long and curved structure in which the anterior end is on the dorsal region of preural centrum 1. Uroneural 2 is almost one half the length of the first, its distal end reaches the distal end of uroneral 1, and it covers a small part of ural 2. Uroneural 3 is the shortest of the series and is located between the distal ends of uroneurals 1 and 2 and the first dorsal principal ray.

Scutes and scales

The entire trunk is covered with ovate cycloid scales and two scute series located on the predorsal and the abdominal edges. The scales are flat, ovate, and deeper than long; they are intensely ornamented with concentric circuli. Unfortunately, it is not possible to recognize the number of scale rows that cover the body trunk of this species.

The predorsal scute series occupies the entire predorsal edge of the body, from the occiput to dorsal fin base. This series includes 18 scutes that increase in size from front to back (Figure 9). Although the firsts ones of these scutes are rather ovoid, slightly longer than wide; those behind them become wider. In dorsal view, those predorsal scutes located in the middle of the series are arrowhead shaped because their middle longitudinal keels are underdeveloped and do not project backward; in contrast, the five posterior predorsal scutes are rectangular, about 3-4 times wider than long, forming lateral wings projected downward from each side of a strong middle longitudinal keel that is projected backward forming a short spine. All these scutes are intensely ornamented with stout and sinuous ridges projected from the middle longitudinal keel.

The abdominal or ventral scute series is located along the ventral edge of the trunk, between the pectoral fin and the anus. This consists of 34 scutes, including 24 prepelvic scutes located between the pectoral and pelvic fins, one pelvic scute located below the pectoral fin, and nine postpelvic scutes located behind (Figure 3). These scutes are four pointed-star shaped, in which the lateral limbs are wide long spatula-like structures, upward projected whereas the anterior and posterior limbs form thick and short keels. The lateral wings of those scutes located in the middle of the abdominal series are so long that cover the ventral half of the abdominal area. In contrast, the scutes located in front and back of this series have smaller lateral wings.