1890.] UPPER CRETACEOUS FISHES. 635 



extremely narrow and deep, the orbit {orb.) relatively large and 

 posteriorly situated, and the surrounding membrane bones well de- 

 veloped. The jaws and facial bones seem to have been almost smooth, 

 the mandible only being marked by a longitudinal series of perforations 

 for a sensory canal ; but the cranial roof is ornamented with numer- 

 ous tuberculations, which are also visible upon the stout preopercular 

 spine. The preopeiculum (p.op.) is comparatively robust, triangu- 

 lar in shape, tapering to a point above, and abruptly truncated 

 below ; its postero-inferior spinous process (s.) exceeds in length the 

 maximum width of the bone, is sharply pointed, and distinctly ap- 

 pears to have been hollow. The operculum (op.) and suboperculum 

 are comparatively thin, the former deeper than broad, and the latter 

 broad in proportion to its depth ; the only ornament exhibited con- 

 sists in a few feeble radiating lines upon the operculum. The 

 branchiostegal rays (br.) are very delicate and apparently numerous. 

 Axial Skeleton of Trunk. — The vertebrae are well ossified, apparently 

 simple double cones, somewhat longer than deep, and about forty in 

 number. The neural and htemal spines are firmly united to their 

 supporting arches, and the ribs in the abdominal region are very 

 robust. There are also numerous short intermuscular bones, in their 

 crushed state transversely overlapping the arches of the axial 

 skeleton. 



Appendicular Skeleton. — The fin-rays are robust, and in all, except 

 the caudal fin, are undivided for a considerable space above their 

 insertion, though apparently articulated and bifurcating distally. In 

 the caudal fin the rays are closely articulated from a point close to 

 the base. In the dorsal and anal fins each ray is borne by a separate 

 interspinous element, but the arrangement of the fin-supports in the 

 caudal is not distinctly shown. The pelvic fins are relatively small 

 and remote, the space between these and the pectorals being three 

 times as great as that between the same fins and the anal. The rays 

 of the latter, about seventeen in number, scarcely exceed those of the 

 pelvic fins in length, but the dorsal fin is relatively much' elevated, 

 with not less than twenty stout rays, and is situated completely in 

 advance of the anal. 



Squamation. — ^The scales are only distinctly shown in part in the 

 type specimen, but it seems probable that they formed a continuous 

 covering. They are all very thin, and their most conspicuous 

 markings are the concentric lines of growth, along which a feeble 

 ornament of fine rugse and tuberculations is developed. A single 

 series of deep narrow scales, at least half as deep as the trunk, 

 occupies the flank ; and above (probably also below) there are 

 smaller, more nearly equilateral scales, likewise of quadrangular 

 shape. 



Formation and Locality. — Upper Cretaceous (Upper Senonian) ; 

 Hake), Mount Lebanon, Syria. 



Evolution of the Aspidorhynchid^. 



The Cretaceous species assigned to Belonostomus are so closely 



