PLE URA CA N THODII 



185 



the tail. Two dorsal fins are present, but apparently no anal. 

 There are paired pectoral and pelvic fins of remarkable structure. 

 No rostral process projects beyond the mouth ; the orbits are 

 surrounded by a double ring of dermal plates, probably formed of 

 fused denticles. Small denticles are distributed over the body ; 

 their histological structure has unfortunately not yet been described. 

 The lateral line runs between two rows of denticles. Broad-based 

 teeth, with a large median and smaller lateral cusps, are closely 



Cladoselache Fyleri, Newb. ; Upper Devonian, Ohio. A, right-side view; B, ventral view; 



C, front view ; restored. (After Dean, from A. S. Woodward, 1'roc. Geol. Assoc.) 



set in rows transverse to the jaws (Fig. 153). The skull resembles 



that of the Notidanidae ; also the jaws, which are amphistylic, 



with a broad palato-quadrate cartilage and long backwardly directed 



hyomandibular. The branchial arches were five, or possibly six or 



seven, in number. The 



notochorcl was probably 



unconstricted ; no centra, 



but neural and haemal 



arches without inter- 



•calaries, have been found. 



The endoskeletal supports 



of the median and paired 



fins are unjointed, extend 



to near the edge of the 



fin-web, and the ceratotrichia are but little developed. Possibly 



this extension is primitive; but it must be noted that it occurs 



also in the Rajiformes and certain other Selachians. The dorsal 



lobe of the caudal fin is borne by segmental radials, and the ventral 



by numerous slender cartilages crowded in its lower half (Fig. 154). 



Fig. 153. 



Teeth of Cladoselaehe, from different regions of the jaws. 

 (After Dean, Fishes I. icing and Fossil.) 



