64 J. W. DATIS ON riSH-KEMAINS TOUND IN THE 



latter are supported by fin-rays. The posterior dorsal is a cartila- 

 ginous fin, presenting the appearance and condition of those found 

 in Sharks. 



The peculiar characteristic of special interest for our present 

 purpose consists in the presence of the bony spines or fin-defences. 

 The pectoral fins are each armed with a strong spine, the exposed 

 part of which is -5 inch in length, the diameter being equal to 

 about one tenth of the length. The posterior face of the spine is 

 straight, the anterior slightly curved, tapering to a sharp point ; it 

 is somewhat flattened laterally, and ornamented with longitudinal 

 striae. On the median posterior surface is a single row of denticles, 

 fourteen in number, extendiug along the whole length of the ex- 

 posed part of the spine ; the denticles are slightly recurved towards 

 the base, pointed, and about equal in length to the diameter of the 

 spine. Attached to and extending behind these spines are the 

 pectoral fins. 



The dorsal spine is about two thirds the size of the pectoral ones. 

 It is straight, pointed, striated longitudinally, and has on its pos- 

 terior surface a single row of short straight denticles, seven in 

 number ; these point towards the base at an angle of 45°. It is not 

 connected with the dorsal fin, but stands alone. It is implanted with 

 a peculiar interlocking joint in a triangular-shaped bone, formed by 

 a prolongation of the bony covering, extending backwards from the 

 occipital region of the head. 



These characters present an analogy with the Convpsacanthus- 

 spines, which appears to indicate a possible relationship between 

 the fossil spines and their modern representatives. 



OsTEACACANTHUS DiLATATTJS, geu. ct sp. nov., Davis. Pig. 3. 



This is a very peculiar form of " Ichthyodorulite " connected 

 with certain other bones which have the appearance of being the 

 exoskeletal plates of a fish. The principal part of this specimen 



Fig. 3. — Ostracacantlius dilatatus^ sp. nov. 

 Spine, nat. size. 



consists of a bony protrusion or spine, which is 1*4 inch in 

 length. The base is imperfect; it now measures -5 inch; had it 

 been perfect, its breadth would probably have been -7 inch. From 



