REPORT ON THE SEALS. 7 



This skull, therefore, had not yet reached a stage in which the possibilities of additional 

 growth in length at the basis cranii were exhausted. In the Challenger specimens from 

 Heard and Kerguelen Islands both the occipito-sphenoidal and intra-sphenoidal synchon- 

 droseswere still unossified,so that if these animals had lived, their crania would undoubtedly 

 have increased in length and in other dimensions. It will be noticed from the measure- 

 ments given in Table I. that though the condylo-premaxillary length in Professor Scott's 

 specimen was more than the same dimension in the Challenger skull from Heard Island, 

 yet that the length to the extreme projection of the occipital crest was greater in the 

 latter cranium. The difference in absolute dimensions between the male and female 

 crania is clearly therefore to be regarded as a sexual differentiation. 



Important sexual characters were seen also in the teeth in the two sexes. In both 



2 — 2 1—1 



the males and females the formula was — incisors 1 _, , canines j~r> post-canines either 



5_5 4_4 



KZIK or JUi' ^though in one female there were six post-canines on one side of each 



jaw. But the relative size of the teeth in the two sexes varied very materially, especially 

 in the canine and incisor teeth. In Table II. I have given the comparative dimensions 

 of some of the teeth in one of the Heard Island males and in the largest female from 

 Betsy Cove, Kerguelen ; all these measurements were taken in a straight line. 



Table II. — Relative Size of Teeth. 



The incisor and canine teeth had conical crowns and elongated single fangs, which in 

 the canine teeth were fluted. The crowns of the post-canines were somewhat laterally 

 compressed, and many of them were marked by shallow, vertical grooves, which indicated 

 a division into two or even three imperfect lobes or cusps ; the fangs were all simple. In 

 the older crania the greatest circumference of the teeth was after they had emerged from 



