1890.] UPPER CRETACKOUS FISHES 631 



and pterygo-quadrate arch are relatively large and expanded laminse, 

 of which the hyomandihular (Plate LY. fig. 3) is the only element 

 well displayed in the fossils underconsideration. The truncated upper 

 extremity of this bone is less than half as broad as its inferior 

 expansion, and a few irregular ridges radiate from the middle of its 

 upper moiety, opposite the point at which the short and stout process 

 (jo.) for articulation with the operculum occurs. The entopterygoid 

 is a long, narrow, lenticular bone, adjoining the upper margin of the 

 short metapterygoid and large ectopterygoid elements (no. P. 3810). 

 There is no definite information concerning the mandibular and 

 maxillary bones, and the only teeth to be observed are very minute 

 slender conical cusps, which seem to have been arranged in clustered 

 series upon a hinder bone of the upper jaw and the splenial (uos. 

 28616 and P. 975 b). Round the eye some very small membrane 

 bones represent a discontinuous or rudimentary circumorbital ring 

 (Plate LIV. fig. 1, CO.) ; and two trapezoidal elements of a large sub- 

 orbital series (s.o.) cover the whole of the space between the circum- 

 orbitals and the preoperculum, while a third irregularly triangular 

 bone adjoins these below. The preoperculum ('p.op.') is of very 

 large size, triangular in shape, terminating in a pointed upper extre- 

 mity almost at the antero-superior angle of the operculum, and gra- 

 dually expanding downwards and forwards, finally bounded by a long, 

 straight or gently curved inferior margin, well beiow the level of the 

 suborbital ring ; the maximum depth of the bone equals somewhat 

 less than twice the length of this margin. The operculum (op.) is 

 also very large, slightly deeper than its maximum breadth, and nearly 

 flat, though bent inwards above. It is irregularly quadrate in shape, 

 and the postero-superior angle is obliquely truncated, so that its 

 upper border is scarcely two-thirds as long as the lower border. The 

 suboperculum (s.op.) is comparatively small, long and narrow, deep- 

 est and truncated in front, and its inferior margin gradually curving 

 upwards to a posterior apex. All the suborbital and opercular bones 

 are ornamented with thick vermiculatiug rugae of ganoine with short 

 branches, as shown in the illustration (Plate LV. fig. 4) taken fi-om 

 the operculum, the arrangement on this bone and on the expanded 

 inferior portion of the suboperculum being more or less concentric 

 with the borders. 



Axial Skeleton of Trunk. — Well ossified vertebrae occur through- 

 out both the abdominal and caudal regions. The centra (Plate LV. 

 fig. 5) are in the form of stout double-cones, but they are always per- 

 forated by a small thread of persistent notochord. The pedicles of 

 the arches seem to be fused with the centra ; and the firmly united 

 neural and hsemal spines are very slender, except the hsemals at the 

 base of the caudal fin, which are much expanded distally (no. 

 P. 975 d). Ribs have not been observed. 



Appendicular Skeleton. — The fins are relatively small, and, so far 

 as known, agree precisely with those of the typical Jurassic Belono- 

 stomus. The rays are stout, laterally compressed, and unarticulated 

 for a short space from their insertion, but soon become distantly jointed 

 and branched. The more robust portions of the rays are also often 

 coated with smooth ganoine. The pectoral fin (Plate LIV. fig. 1, 



