CLASP ERS 



129 



of the derivation of the girdle from the base of the radials, and is 

 conspicuous in the Pleuracanthodii (p. 181), in the Notidani, and 

 to a less extent in many sharks, but is lost in the Dipnoi. The 

 Holocephali, however, have the radials of the pelvic fin radiating 

 from the edge of a single basal plate, like a fan (Fig. 54, B). 



The fossil Elasmobranchs give little or no help for the interpre- 



Dorsal view of the pelvic girdle and tins of a male Acanthias vulgaris, ilisso ; the skeleton 

 lias been exposed on the right side, a, axial cartilage of clasper ; bp, basipteryginm ; b.iu, cut 

 body-wall ; r, dorsal covering plate ; e, ventral plate ; h, hook ; os, opening of glandular sac ; 

 p, pelvic girdle ; pi; propterygial, or anterior basal ; pt, posterior radial ; pv, pelvic fin ; 

 r, modified radial ; s, outline* of glandular sac embedded in body-wall dorsal to girdle ; sty, 

 hard style. 



tation of the skeleton of the paired fins. The fact that the pectoral, 

 as a rule, differs so much from the pelvic, shows that one, or 

 both, have departed considerably from the primitive type 

 (p. 108). 



We may here describe the modifications of the skeleton of 

 the pelvic fin brought about by the development of the " clasper," 

 mixipterygium, or copulatory appendage of the male (Gegenbaur 

 [155], Petri, Jungersen [254-5], Huber [222]). The pelvic fin- 



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