BY WILLIAM A. HASWELL, M.A., B.SC. HI 



Pelvic Fins. (Plate II., fig. 5.) 

 The pelvic arch is very slender and very wide from side to side, as 

 in Rays generally. Its lateral extremity presents two articular 

 surfaces, one for the propterygium (pre-axial fin-ray) the other for 

 the metapterygium. The mesopterygium is not represented. In 

 front of the articulation a strong compressed process extends 

 forwards and outwards, and behind on the dorsal surface just over 

 the two articulations is a very prominent, slender, curved process 

 which extends backwards and upwards. The propterygium con- 

 sists of a long and three short joints, the last bearing several 

 rudimentary fin rays. The metapterygium consists of a long basal 

 joint and three shorter distal segments ; it bears twenty-four rays 

 none of which are bifurcated. 



Unpaired Fins. 



The dorsal fin is small, with about fourteen rudimentary rays 

 supported on two elongated, laterally compressed cartilages, the 

 continuity of which with the spinous processes is manifest. The 

 anal is very similar to the dorsal. The caudal is rudimentary. 



The dorsal fin is described and figured by Mivart, 1. c, p. 454, 

 pi. LXXV1IL, fig. 6. 



SUMMARY. 



In the following summary are enumerated the principal 

 characteristics of the skeleton in such families of the Plagiostomi 

 as I have had the opportunity of examining. The division of the 

 Selachoidei into two principal sub-orders — the Palceoselachii and 

 the Neoselachii — seems to me to follow as a necessary conclusion 

 from the researches of Gegenbaur on the anatomy of the skull. 

 The prefixes have reference, I need hardly add, not to the relative 

 geological age of the two groups, but to their relative degree of 

 specialisation ; the structure of Notidanvs is certainly much more 

 archaic than that of any other Shark. 



