SEXUAL CHARACTERS ELASMOBRANCH FISHES 201 



clasper formed by the overlapping edges is very short. On the 

 inner side of the dorsal surface of the clasper is a sht whose 

 cavity leads not forwards, but slightly backwards, and hence 

 cannot be truly regarded as a pseudosiphon. 



PRISTIURUS MELANOSTOMUS 



The black-mouthed dogfish 



This near relative of Scylhum differs from that genus more 

 than might be supposed. The specimen examined, one of two 

 from an unnamed locaUty, measures 62 cm. in length. The 

 siphons are long and narrow, in this case 12.5 cm., poorly de- 

 veloped, with but feebly muscular walls. They are propor- 

 tionately longer than in Scyllium, but lie immediately under the 

 skin as in Acanthias. The claspers terminate in a gimlet-like 

 coil (fig. 2), which, when unrolled, as in the inset, show^s slight 

 indications of a rhipidion. The actually closed portion of the 

 scroll-like clasper is moderately long as in Scyllium. 



CHIMAERA MONSTROSA 



The king of the herrings, or rabbit fish 



Although the HolocephaU are not strictly elasmobranchs, it is 

 both important and essential that they should be included, since 

 they exhibit the features which form the subject of this investi- 

 gation. They possess the peculiarity of an anterior pair of 

 claspers, or grapplers, in front of the pelvic fins in addition to 

 the usual posterior pair. The anterior claspers are capable of 

 being retracted into a glandular pouch, where they are usually 

 held in retreat. They are absent in the female, but the pouch 

 may in some cases be present in a rudimentary form. There 

 is also a frontal clasper in the male. In Harriotta the claspers 

 are said to be poorly developed, and the frontal clasper absent. 



The specimens here described are from a batch of about nine 

 received from Rockall, September, 1920. 



In the females, the largest of which is 79 cm. long, I failed to 

 find any vestige or rudiment of either anterior claspers or their 

 pouch: there appears to be no trace of them, at any rate in the 

 present species, Chimaera monstrosa. 



JOURNAL OP MORPHOLOGY, VOL. 39, NO. 2 



