FINS OF ELASMOBEANCHS. 455 



The median cartilages are exceedingly small, and are also twelve in number. They 

 are all of subequal length, and shorter than any of the distal cartilages except the 

 first. 



The first median cartilage is more extended antero-posteriorly than are the others. 

 They gradually decrease in size postaxiad from the first. 



The more preaxial of the two hasal cartilages, the more preaxial of the two large 

 cartilaginous plates, is very elongated and subquadrangular in shape. It supports the 

 first five median cartilages and part of the sixth. The other basal cartilage is subtri- 

 angular, with one angle ventrad. It supports part of the sixth median cartilage and all 

 the more postaxial ones. 



These two cartilages are evidently serial homotypes of the dorsal portions of the 

 cartilaginous plates which are situated preaxially and postaxially to them. The latter 

 are continuous with the interneural axial cartilages ; but the basal cartilages of the dorsal 

 fin show more or less evidence of segmentation existing between them and the inter- 

 neural cartilages which ventrally support them. 



RAIA MACULATA. 



Dorsal Fin (Plate LXXVIII. fig. 7). 



Here there are two elongated basal cartilages which support radials, many of which 

 bifurcate. 



The more preaxial basal cartilage is much the larger, and lies upon the interneural 

 axial plates. It may be said to support nine radials, of which the seventh and ninth 

 bifurcate distally. 



The more postaxial basal cartilage supports postaxially one single radial and a large 

 cartilage which ends distally in six filamentary prolongations. 



Another, much-divided radial is supported by the dorsal margin of the more postaxial 

 basal cartilage. 



The resemblance presented by these radials, with their supporting basal cartilages, to 

 the cartilages of the ventral fins of Sharks is striking, with the exception of the distal 

 bifurcations and subdivisions which here exist. 



CALLORHYNCHUS ANTAECTICUS. 

 First Dorsal Fin (Plate LXXIX. fig. 1). 



The first dorsal-fin skeleton closely resembles that of Chimcera, and exhibits a degree 

 of concentration exceeding that of the spine-bearing Elasmobranchs Acanthias and 

 Spinax. It consists of one single triangular plate only, which is probably articulated 

 ventrad by its apex to a cartilaginous upgrowth of the vertebral column, and bears in 

 front of it a very elongated spine. This plate, when compared with the dorsal fin- 

 skeleton of the genera just mentioned, seems to answer to the basal, median, and distal 

 cartilages all fused together into one mass. 



VOL. X. — PART X. No. 3. — February \st, 1879. 3 q 



