30 PISCES. 



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. The notochord must have 

 been unconstricted, without calcifications in the sheath ; and 

 the endoskeletal cartilages are permeated with minute granular 

 calcifications. The teeth are conical cusps upon broad bases, 

 several series functional at the same time. A ring, of dermal 

 plates surrounds the eye ; but there are no membrane-bones. 



Detached teeth resembling those of Cladoselache have long 

 been known from Carboniferous formations under the name of 

 Cladodus ; but there is reason to believe that several primitive 

 genera perhaps even more than one i'amily or order were 

 characterized by teeth of this form, and it is therefore useless 

 to discuss the distribution of such fragmentary fossils. It 

 suffices to enumerate the known characters of 



Cladoselache (figs. 21, 24, 25). The fish is elongated and round-bodied, 

 with a short blunt snout and forwardly placed eye. The precise cha- 

 racters of the cranium are unknown; but the olfactory capsules are 

 large, placed close together, and terminal. The mouth is also terminal, 

 the upper and lower jaws being similar in shape and size, and sup- 

 ported by a slender elongated hyomandibular. The teeth are largest, 

 longest, and most acutely pointed at the symphysis of the jaw, smallest 

 and shortest at the angle of the mouth. The transverse series are 

 closely apposed, and not separated as in the modern Chlamydoselache ; 

 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 

 successor 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 paired fins have already been described 

 (p. 24, fig. 21). Two low dorsal fins have been observed (the pos- 

 terior only shown in fig. 24), 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 (fig. 25) 

 is strongly heterocercal and very remarkable. The neural arches (N) 



