920 



MK. B. LTDEKKBB ON A 



[Nov. 14, 



The extreme shortness of the skull (only a very small portion 

 of the tip of the rostrum bemg missing) indicates the wide 

 difference of the genus from Sqnalodo7i ; and we thus have evidence 

 that the Squalodonfidce, hke the Delphinidcp, were represented by a 

 long-beaked and a short-beaked group. The question will there- 

 fore arise whether the two groups of the last-named family may 

 not be independently derived from the two corresponding groups 

 of the Squalodonts. 



Fig. 1. 



Upper surface of a skull of Prosqualodon australis, from the Tertiary deposits 

 of Chubut, Patagonia. Fr., frontal; mx., maxilla; Pmx., premaxilla; 

 Exo., Bupra-occipital ; Pa., parietal. 



1 a, Narial region of specimen in the La Plata Museum. 



Be this as it may, the general characters of the fossil skull are 

 essentially those of modern Dolphins, asymmetry being but slightly 

 developed, while the proximal extremities of the premaxUlae and 

 maxillae overlie and conceal the frontals to the same extent. The 

 premaxillaB, although their vomerine borders are perhaps slightly 

 imperfect distally, seem, however, to have roofed over the mes- 

 ethmoid channel to a less degree than in existing Dolphins, thus 



