104 WEALDEN AND PURBECK FOSSIL FISHES. 



posterior being the smaller and triangular in shape with a short antero- superior 

 process, the anterior elongate-triangular slowly tapering to a point in front. The 

 premaxilla has an oral border scarcely more than one-quarter as long as that of 

 the maxilla, but its styliform teeth are somewhat larger; its upper portion near 

 the middle line of the snout rises into a process for articulation with the ethmoidal 

 region of the skull. The mandible tapers gradually from the low coronoid eleva- 

 tion behind to the bluntly pointed symphysis in front. The articulo-angular bone 

 (ag.) is very short, with its finely rugose ornament slightly more conspicuous than 

 that of the dentary (d.), which is marked chiefly by the row of large pores along 

 the course of the slime-canal. Its blunt teeth, which are somewhat stouter than 

 those of the maxilla, seem to be in more than one series at the symphysis. 



The opercular bones are so thin that they are usually much broken in the fossils, 

 and their fine rugose ornament is so delicate that it is often destroyed. The 

 operculum (PI. XX, fig. 6; PI. XXI, fig. 4, op.) is a little deeper than wide and 

 slightly more than twice as deep as the suboperculum (sop.), which bears a con- 

 spicuous sharply pointed antero-superior process. The triangular interoperculum 

 (iop.) is relatively large. The preoperculum {pop.), which tapers upwards nearly 

 to the upper limit of the operculum, is a narrow plate, not much expanded at its 

 blunt angle, and almost without a horizontal limb. It is traversed by a very 

 large slime-canal, from which a few branchlets radiate backwards over the lower 

 expansion. The upper branchiostegal rays (br.) are large and finely rugose, and 

 all these rays seen in the fossils, not less than 16 pairs in regular series, are rather 

 broad laminae. 



The delicate vertebral rings in the caudal region, with their short recumbent 

 neural and hasmal arches, in the type specimen, have already been mentioned. 

 Other specimens show that the centra are represented only by rings throughout the 

 vertebral axis ; and in some cases a ring appears to consist of two separate parts, a 

 pleurocentrum above and a hypocentrum below (B. M. no. P. 3605 <>). The ribs 

 are short and slender (B. M. no. 4:3038). 



The supratemporal and post-temporal plates have not been well observed, but 

 they are evidently thin and very faintly rugose. The supraclavicle (PI. XXI, fig. 

 4, scl.) is about three times as deep as wide, and crossed obliquely by the large 

 slime-canal, above which its posterior margin is enamelled and pectinated. The 

 sigmoidally bent clavicle (cl.) is nearly smooth in its narrow exposed portion, but 

 rises into a triangular rugose boss just beneath the notch for the insertion of the 

 pectoral fin, and then passes below into a large smooth expansion where it is 

 covered. The postclavicular plates, or perhaps anterior scales, are smooth for the 

 greater part of their width, but pectinated and serrated at their posterior 

 margin. The pectoral fin (PI. XXI, fig. 4, pet.) comprises about 20 rays, all 

 articulated and divided distally, and the foremost fringed with a close series 

 of small, deeply overlapping fulcra. The pelvic fins (plv.), which are inserted 



