EASTMAN: TYPES OF FOSSIL CETACEANS. . 89 



maxillarics on either side of the narial openings, but these bones are flattened 

 here, and rather widely expanded. Lophocetus shows the same squarish excava- 

 tion of the maxillaries on either side of the vertex that occurs in modern Iniinae, 

 and also in Pontistcs and Iniopsis, but in none of these do the maxillary fossae 

 have such prominent borders. A peculiar feature of Lophocetus, as compared 

 with both recent and fossil Iniinae, is that the prominence formed by the nasals 

 and frontals immediately behind the narial apertures is deeply cleft in a longitud- 

 inal direction. Moreover, in Inia this eminence is formed almost entirely by the 

 frontals, which enclose the interparietal between their upturned borders pos- 

 teriorly, and completely cover the nasals at the vertex in front. But in Lophoce- 

 tus the frontals scarcely appear in this region, and the divided, nodulose nasals 

 are conspicuously developed, alone forming with the mesethmoid the posterior 

 wall of the external nares. This wall is relatively broader and less convex in a 

 transverse direction than in Inia, but by no means presents the well-defined quad- 

 rate surface that is so strongly marked a feature of Iniopsis. The characters of the 

 basicranial axis, and especially the arrangement of palatine and pterygoid elements, 

 point to a closer relationship with Inia than with any known fossil form. 



It is to be regretted that, owing to the imperfect condition of the specimen, 

 comparisons cannot be made between Lophocetus and other Iniinae with respect to 

 the dentition and extremity of the snout. One is perhaps permitted to infer from 

 the general agreement in other respects that the dentition had become polyodont- 

 homodont, and that teeth were still borne by the extremity of the premaxillary. 

 The deep fissure separating these last-named bones in advance of the mesethmoid 

 is probably without greater significance than the fused condition of the inter- 

 parietal, both of which are regarded as old-age characteristics. On the whole, 

 considerable reason is found for supposing Lophocetus to belong to the ancestral 

 line from which modern Iniinae are directly descended. Saurodelphis, on the 

 basis of its dentition, would be regarded as more primitive than any of these 

 forms, and Eurhinodelphis, with its edentulous premaxillary resembling that of 

 Ziphioids, would be considered more highly specialized. Further material is 

 necessary, however, before one can speak confidently in regard to the direct line 

 of succession. We may conclude this part of the discussion by reproducing the 

 scheme devised by Abel 1 for showing at a glance his views of phylogenetic and 

 other relations. 



1 Mem. Musee Roy. d' Hist. Nat. Belg. 1901, 1 : 39. 



