Hi; WEALDEN AND PURBECK FOSSIL FISHES. 



fig. '.'. enpt) is a relatively large delicate lamina of bone, while the ectopterygoid 

 (ecpt.) forms a stout bar at its lower border in front of the quadrate. The 

 maxilla and premaxilla are unknown. The mandibular ramus (md.) is especially 

 short and deep, and its dentary portion must have been comparatively small. 

 There seem to be traces of minute conical teeth near the front of both jaws. 



The operculum, displayed partly from within, partly as an impression in 

 PL XXIII, fig. ( .) (op.), is not less than two-thirds as wide as deep, and narrowed 

 towards the upper end. Its outer face is somewhat convex, and quite smooth, 

 though marked by a feeble waviness concentric with the lines of growth. The 

 suboperculum and interoperculnm are comparatively small : the former is much 

 widci- than deep, while the latter seems to taper upwards into a point between the 

 operculum and preoperculum. The preoperculum, seen from within in PI. XXIII, 

 fig. 9 (pop.), is sharply bent at the expanded angle, the tapering upper and lower 



Fig. 36. — Pleuropholis formosa, sp. nov. ; restoration, somewhat enlarged.— Lower Purbeck Beds; Teffont, 



Wiltshire. 



limbs being nearly equal in size and at right-angles to each other. It is traversed 

 by a conspicuous slime-canal, from which two or three straight branches radiate 

 backwards at the angle. There are trace's of large branchiostegal rays below the 

 interoperculnm. 



The axial skeleton of the trunk is usually obscured by the thick squamation, 

 but delicate cylindrical vertebral centra are observable in some broken specimens 

 discovered by the Rev. W. R. Andrews (B.M. no. P. 9851). 



Each of the pectoral fins comprises a dozen rays, of which the length of the 



longest about equals that of the head without operculum. Near its base the 



fringing fulcra are normal, but in its distal half they are more widely spaced and 



each bears an ovate expansion at its apex (PL XXIII, fig. 10). The pelvic fins are 



only about two-thirds as large as the pectorals, with not less than rays and 



normal slender fulcra. The dorsal and anal fins are about equally elevated, with 



L rays respectively, of which the length of the foremost is less than the 



the trunk at its insertion. As shown when the squamation is removed 



Kill, fig. 11), each ray is separated from its corresponding support by a 



intercalated rod, as in the existing Amia. All the rays bifurcate once or 



'tally, with wide articulations. As in the type specimen, the fulcra are 



