1^99.] 



SHABK-TOOTHED DOLPfilN FEOM PATAGONIA. 



921 



leaving in the dry skull the greater extent of the vomer exposed, very 

 much as in Cogia. In life the exposed mesethmo-vomerine channel 

 was doubtless occupied by a large mesethmoid cartilage. It is 

 much to be regretted that the narial region of the British Museum 

 specimen is imperfect, the nasal bones being wanting. I have there- 

 fore had reproduced (fig. 1 a, p. 920) this region from my original 

 plate, from which it will be seen that the nasal bones, instead of 

 being reduced to irregular nodules lying in depressions of the 

 frontals, forin a slight penthouse to the upper end of the blow-hole. 

 In my original paper I stated that the molariforra teeth were 

 double-rooted, like those of Squalodon ; but a detached specimen 

 (fig. 2 a, p. 921) shows that the two fangs have coalesced, although 

 separated by a deep groove. And it appears that the same feature, 



Fig. 2. 



Lateral aspect of the specimen of ProsqiMlodon austraUs represented in fig. 1. 

 2 a. A molar tooth associated with the skull. 



judging from the sockets, obtains in all the teeth of this type. 

 Some of the hinder molars were, however, siugle-f anged ; and the 

 whole number of teeth did not apparently exceed ten or eleven 

 pairs in each jaw, against the fifteen pairs of Squalodon. Whether 

 the anterior teeth were of the slender incisiform type of the 

 similarly situated teeth of Squalodon cannot be ascertained. The 

 cusps on the molars are less developed than in the latter. 



The new specimen accentuates the distinction of Prosqualodon 

 from the last-named genus ; and whereas in the structure of the 

 nasals the South-American genus is the more generalized of the 

 two, in the characters of the teeth it is the more specialized. 

 It is. worth mention that the retention of roofing nasals in Pro- 

 squalodon and in a second Patagonian genus, for which I have 

 suggested the name Argyrodelphis, removes any difficulty, so far 



