DEVONIC FISHES OF THE NEW YORK FORMATIONS 55 



they are indeed tightly wedged together, and the cusps are frequently 

 much abraded by wear. Every tooth has a principal cusp with variable 

 smaller lateral cusps, and the broad base of each is overlapped by its suc- 

 cessor behind. The number of gill arches is uncertain, but five are known, 

 and the presence of one or two others is suggested by some specimens. 

 The neural and haemal arches of the axial skeleton have been observed 

 only in the caudal region, where they are short tapering rods of cartilage, 

 bifurcated at the base and distinctly corresponding in number with the 

 calcified remains of the muscle plates. Intercalary cartilages are wanting. • 



The small basal cartilages of the paired fins seem to be embedded in 

 the body wall, and the unjointed radial cartilages extend directly outwards 

 to the edge of the membrane. There are no claspers in the pelvic fins, 

 and both these and the pectoral fins were probably mere balancers, directed 

 somewhat downwards. Two low dorsal fins have been observed, both 

 destitute of an anterior spine,' but strengthened by simple cartilaginous 

 rays extending to the edge of the fin membrane. No anal fin has been 



distinguished. The caudal fin [text fig. 14] is strongly heterocercal and 

 very remarkable. The neural arches seem to persist even to the end of 

 the upturned axis, directly supporting the thick radial cartilages of the 

 superior lobe of the caudal fin. The dermal membrane of the inferior lobe 

 of the caudal fin is supported by simple cartilaginous rays only in its lower 

 portion where they extend quite to the margin. The eye is surrounded by 

 a double series of small dermal plates ; but the remainder of the fish is 

 covered only with minute lozenge-shaped denticles, which are apparently 

 not enameled. The latter are slightly enlarged at the angles of the mouth, 

 where they approximate in size and shape to the smallest of the teeth. 

 The lateral line extends along the trunk between two series of the shagreen- 

 like granules, and was thus presumably an open canal. A short dermal 

 expansion forms a horizontal keel on each side of the caudal lobe just in 

 advance of its upturned end. The largest known examples measure nearly 

 2 meters in length. 



We have said that this genus is looked upon as furnishing important 



"This statemenc requires to be amended. D- Dean having discovered at least one 

 specimen in which the anterior dorsal fin is provided with a powerful Ctenacanthus like 

 spine. 



