ASPIDORHYNCHUS. 97 



1. Aspidorhynchus fished, Egerton. Plato XX, figs. 1 — 4. 



1854. Aspidorhynchus fisheri, P. M. G. Egerton, Ann. Mag. Nat. Hist. [2], vol. xiii, p. 434. 



1855. Aspidorhynchus fisheri, P. M. Gr. Egerton, Figs, and Descripts. Brit. Organic Remains (Mem. 

 Geol. Surv.), dee. viii, no. 6, pi. vi. 



1880. Aspidorhynchvs fisheri, A. Giinther, Introd. Study of Fishes, p. 369, tig. 146. 



1895. Aspidorhynchus fisheri, A. S. Woodward, Catal. Foss. Fishes, Brit. Mas , pt. iii, p. 425. 



Type. — Nearly complete fish ; Dorset County Museum, Dorchester. 



Specific Characters. — A slender species attaining a length of about 40 cm. 

 Maximum depth of trunk equalling about half the length of the head with 

 opercular apparatus, which is comprised nearly four-and-a-half times in the total 

 length of the fish. Cranium rapidly tapering to the acute rostrum, which is 

 produced in advance of the mandible to an extent equalling one-third of the total 

 length of the cranium ; cranial bones and cheek-plates ornamented with fine 

 granulations, which are fused into longitudinal rugae on the rostrum and some- 

 times fused or raised on ridges on part of the cranial roof ; mandible and opercular 

 bones almost smooth, the former only marked by the openings of the slime-canal ; 

 presymphysial bone very short, scarcely longer than deep ; mandibular teeth 

 comparatively stout. Pelvic fins arising midway between the pectorals and the 

 caudal. Scales smooth or very feebly rugose, except those of the dorsal region, 

 which are marked with longitudinal rugee. 



Description of Specimens. — The type specimen (PI. XX, fig. 1) shows the general 

 proportions of the fish, but it is much broken and flaked, and various details of 

 structure are better seen in the other specimens. It exhibits portions of all the 

 fins, indicating their relative positions. It also displays well the arrangement of 

 the scales. 



The rostrum, which is closely ornamented with longitudinal ridges, is apparently 

 complete in the type specimen and must have occupied about one-third of the total 

 length of the skull. The rest of the skull, however, and the mandible are better 

 seen in a smaller fossil in the British Museum (enlarged in PI. XX, fig. 2). The 

 greater part of the cranial roof is formed by the large frontal bones (/>"•), which 

 are united in a very wavy median suture, and are only slightly excavated at the 

 outer edge by the orbits. They are externally ornamented by fine tubercles, which 

 are arranged in radiating lines, sometimes on ridges, sometimes themselves fused 

 into short ridges. They are also marked along each outer border by the groove 

 and series of pores forming the openings of the slime-canal. The parietals {pa.) 

 are short and broad, crossed behind by the groove of the transverse slime-canal, 

 and ornamented with tubercles which are more or less fused into antero-posterior 

 ridges. A crushed mass (x.) behind the parietals is probably to be interpreted as 

 the fused epiotics. A slender parasphenoid (pas.) is seen crossing the orbit. Of 



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