ELASMOBRANCHII PLEUROPTERYGII 



437 



detected. The exoskeleton consists of minute lozenge -shaped 

 denticles, which invest the body and extend on to the surfaces 

 of the fins, and there is also a circurnorbital ring of several con- 

 centric rows of small square plates. A lateral line, in the form 

 of a groove between two rows of denticles, extends along each 

 side of the body. The notochord is persistent. Calcified neural 

 and haemal arches (basidorsals and basiventrals) have been ob- 

 served in the caudal region, where they correspond numerically 

 with the remains of the myotomes, but interdorsal or inter- 

 calary arcualia seem to be absent. The upper and lower jaws ; 



FIG. 249. Restoration of Cladoselache fyleri. Lateral and ventral views. 

 (From Parker and Haswell, after Dean.) 



similar in size and shape, are apparently supported by a hyo- 

 mandibular cartilage ; hence the skull is hyostylic. The endo- 

 skeletal supports of the pectoral, and especially those of the 

 pelvic fins, exhibit a more primitive disposition than in any 

 other Fishes. They extend nearly to the distal margins of the 

 fins, where they seem to interdigitate with the proximal ends of 

 feebly-developed ceratotrichia (Fig. 145). The extension of the 

 fins in the horizontal plane, the gradual shading off of their 

 broad bases into the sides of the body, and the resemblance 

 between their radialia and those supporting median fins, are very 

 suggestive of the origin of the paired fins from continuous lateral 

 fin-folds. Claspers are absent. The dentition is well developed, 

 and several rows of teeth seem to be functional at the same time. 



