104 STUDIES ON THE ELASMOBRANCH SKELETON", 



the skull. These are inclined downwards and backwards and 

 may represent upper labial cartilages, or may perhaps be regarded 

 as representing a rudimentary rostrum. 



The anterior vertebral plate presents laterally very broad and 

 long wings representing the coalescent and produced transverse 

 processes. In the middle it presents a prominent vertical lamina 

 formed of the coalescent spinous processes. This ends some distance 

 in front of the position of the shoulder girdle, with which it has no 

 connection. There are thirty pairs of ribs, of which the majority 

 are of considerable length. 



HYPNOS SUBNIGER. 



Plate XL, Figs. 6-9. 



Skull and Visceral Arches. (Plate XL, figs. 6 and 7.) 



In general shape the skull recalls to some extent that of 

 Heterodontus. It is long, rather narrow and high, broadest behind 

 in the occipital and auditory regions, narrower between the orbits 

 and becoming broader again in front in the olfactory region. The 

 foramen magnum is very large ; its plane is very oblique, and a 

 large space occupied only by membrane intervenes between the 

 upper border of the foramen and the commencement of the neural 

 arches of the vertebra?. The condyles, as in Torpedo, are placed 

 close to the foramen magnum. As in Torpedo, also, the aperture 

 for the vagus is very large. Immediately above and a little in 

 front of it is a short but well-marked process directed outwards ; 

 this is rudimentary in Torpedo. Below and behind the foramen 

 the postero-external angle of the skull is drawn out into a 

 dorso-ventrally compressed process with the extremity of which the 

 basal cartilage of the first branchial arch articulates. This is an 

 arrangement which seems, so far as I have observed, to be peculiar 

 to this genus. As in Torpedo, the articular surface for the hyo. 

 mandibular is long, narrow, and nearly horizontal, situated low 

 down nearly on a level with the base of the skull. The elevation 



