1868.] EGERTON LIASSIC FISHES. 501 



A few obsolete strite are visible here and there iii some of the speci- 

 mens, terminating in a slightly notched margin ; but as this charac- 

 ter is very limited in extent, it can hardly be considered of specific 

 value, as far as the present evidence extends. This genus belongs 

 to the Sauroid family of the Ganoid order of Agassiz. 



IsocoLTJM GRANULATUM, gen. ct spcc. nov., Egerton. 



This is another novelty from the Lias of Lyme Regis, also in the 

 collection of the Earl of Enniskillen. As the anterior part of the 

 head is deficient it is impossible, in the absence of the teeth, to say, 

 with any certainty, to what family it belonged. It has some resem- 

 blance to the larger species of FhoUdopJiorus found in the Solenhofen 

 slates, but more to the Sauroid genus Caturus. Eor elegance of 

 form this fish can vie with a Salmon of modern time, the contour of 

 the two being very similar. The specimen is unique. It measures 

 18 inches in length, the snout and tail being both wanting. The 

 head is small, occupying about one-fifth of the length. The shape of 

 the body is fusiform or, rather, elliptical. The dorsal fin occupies the 

 exact centre of the back, and the ventral fins a similar position on 

 the ventral surface. The anal fin is central between the ventral 

 fins and the tail. The depth of the body at the dorsal fin is 4^ 

 inches ; and the contours of the fish converge gradually and symme- 

 trically fore and aft, until the diameter at the shoulder-girdle is 

 3 inches and at the tail 2 inches. The opercular apparatus is rather 

 slight. The component plates are finely granulated on the surface. 

 The column contains forty-six vertebrae well ossified. The spinous 

 appendages are slight in the fore part of the column, but behind the 

 dorsal fin above and the vent below they assume a fuU and vigorous 

 development. In advance of the dorsal fin there are twenty inter- 

 spinous bones not bearing dorsal rays ; a similar arrangement occurs 

 in Caturus, Thrissops, and some other fossil forms, as well as in 

 Lepidosteus, the Clupeidce, and other recent fishes. These are suc- 

 ceeded by seventeen large interspinous bones, bearing the rays of the 

 dorsal fill ; the two or three anterior rays are short, and above 

 these fulcral rayst he margin of the fin is finely fringed ; the 

 fifth ray is the largest, but the entire fin is small compared with 

 the size of the fish ; the rays are cross-jointed at the extremities, 

 but not bifurcate. The pectoral fins contain twelve rays each, the 

 first being very stout and triangular in section ; they correspond with 

 the rays of the dorsal fin in being cross-jointed in their distal parts 

 and not split. The ventrals have a tolerably strong pelvic support 

 nearly an inch in length ; the fins are comparatively large, measuring 

 1| inch in length, and being composed of twelve rays each ; unlike 

 the other fins, their rays are bifurcate at their extremities. The anal 

 fin occupies a central position between the ventral fins and the tail ; 

 it contains ten short rays articulated to ten strong interspinous 

 bones. The caudal appendage is wanting, but, guided by the large 

 size and spatulate form of the last vertebral processes, it is presuma- 

 ble that it was an organ of great power. The scales are of moderate 

 dimensions, not so thick as those of Eugmithus, Osteorachis, and other 



