52 



ON THE APPENDICES GENITALES (CLASPERS) IN THE SELACHIANS. 



more, and that the M. extensor is single. The glandular body is prolonged into the shaft quite as 

 in Torpedo. 



Rhinobatidce. 



Rhinobatus columnae Bonap. 

 (PI. Ill, fig. 35-370 



In a specimen of the total length of 85,5™ and a breadth of 26™ across the pectorals the 

 appendix had a length of n,5 cm . 

 The other measures were: 



from the fore end of the slit to the hindmost point of the appendix 7A cm 



the part free of the fin 6,2 cm 



Length of the terminal part i,9 cm 



Breadth - - - o,8 cm 



The appendix reminds of that in Torpedo, being flat, and having 

 (on the ventral side) the terminal part marked off by a slight constriction; 

 but it is considerably longer, with a long free portion, and a relatively 

 short terminal part, and so it has a rather slender, elegant appearance. 

 The ventral side is all covered with the same dense mosaic of fine, flat' 

 dermal teeth as the other parts of the belly; only the very outmost point 

 (i mm ) is naked and soft. On the dorsal side the region around the fore- 

 most part of the appendix-slit is naked as well as the whole part before 

 the slit, which is normally in contact with the belly, this having also a 

 corresponding naked spot; furthermore the naked part stretches as a 

 small stripe backward close to the medial edge until the terminal part, 

 the dorsal side of which is quite naked; otherwise the dorsal side is co- 

 vered with teeth , and has the darker colour of the back of the animal. 

 The appendix-slit is situated quite close to the lateral edge, only in the 

 terminal part it bends towards the middle. On the dorsal side of the 

 terminal part are seen two < marginal-slits > leading into pockets, quite 

 corresponding to those in Torpedo and Nardil e; the medial one is the 

 longer; in the lateral one the outermost part of the piece T, is seen freely 

 protruding from the skin as a shining thorn. 



The skeleton. Between the basale and the appendix-slit are 

 found four pieces: b t , 6 2 , b i , b A \ the last one being the longest, next to that follows b l which is also 

 the broadest, but they are all more long than broad; b 3 and b 4 bear no rays, b 2 bears the last ray, b l 

 the last but one (and, in connection with the basale, also the last but two). The piece jl is exceed- 

 ingly long; anteriorly it articulates with the dorsal side of b l close to the basale, then it stretches 



Fig. 22. 



Rhinobatus columnar. 

 The left appendage from the 

 dorsal side. Natural size. F 

 the fin-membrane. /' the 

 opening of the lateral pocket, 



/ of the medial one. 



