86 FOSSIL FISHES OF THE ENGLISH CHALK. 



series above that which forms the ventral border of the flank, its ridges quite 

 smooth. 



Description of Specimens. — The type specimen in the Mantell Collection 

 (no. 4033) is very imperfect, and not accurately represented in the figure published 

 by Agassiz. It shows only fragments of the head, and lacks the dorsal part of the 

 trunk. The right pelvic fin is mistaken for the pectoral by Agassiz ; and hypo- 

 thetical indications of the supposed pelvic and anal fins are added to the original 

 drawing just mentioned. The mandibular ramus is wrongly restored, and 

 imaginary teeth are represented ; while the caudal vertebral centra are consider- 

 ably too long in the drawing. The enlarged figures of the scales are more nearly 

 accurate. 



The best known example of the species (PL XIX, fig. 3) is in the Woodwardian 

 Museum, Cambridge, but this specimen resembles the type in lacking the dorsal 

 region of the trunk. Other specimens in the British Museum are more imperfect, 

 but reveal some of the principal characters of the fish. The head seems to be about 

 half as long as the trunk, which is moderately elongated with a rather deep caudal 

 pedicle. 



The cranium as seen from above (fig. 3 ft) is triangular in shape, and its 

 greatest width at the occiput equals about two-thirds of its length. The supra- 

 occipital bone (socc.) is relatively small, with a median vertical crest on its hinder 

 face. Its upper portion enters the cranial roof, but does not completely separate 

 the parietals {pa.), which are much extended antero-posteriorly and meet in the 

 middle line for more than half of their length. The squamosal-pterotic region (sip) 

 also seems to be relatively large, but sinks into a fossa which would be originally 

 occupied by a forward extension of the lateral muscles of the trunk. The frontals 

 (/V.) are very large, widest between the eyes, where they expand into a supraorbital 

 flange on either side. They taper rapidly forwards, where the small mesethmoid 

 (fth.) projects beneath them. None of these bones are ornamented. 



The mandibular suspensorium is only slightly inclined forwards, so that the 

 articulation of the mandible is beneath the hinder border of the orbit. The 

 hyomandibular is narrow and deep. The ectopterygoid (seen in B. M. no. 47932) 

 is a long, narrow lamina of bone, its posterior end bending doAvnwards along the 

 anterior border of the quadrate. The premaxilla is relatively small, occupying the 

 anterior quarter of the toothed edge of the upper jaw, tapering to a point behind, 

 turned up into a short ascending process in front. The maxilla (fig. 3, ma?.) is 

 arched and shaped like that of Glupea. Its exposed face is smooth, and its upper 

 border is overlapped by two large supramaxillse (fig. o, smx. 1, 2), which are also 

 nearly smooth. Both the premaxilla and maxilla bear clustered minute conical 

 teeth. The mandible is shaped as in Gtenothrissa, with a comparatively long and 

 deep coronoid region, a short tooth-bearing margin, and truncated symphysis; in 

 fact, quite unlike the hypothetical sketch published by Agassiz. The mandibular 



