EASTMAN: TYPES OF FOSSIL CETACEANS. 83 



tively broader in the fossil form than in Inia, but otherwise the bones forming 

 the basicranial axis are remarkably similar. It is to be regretted that injury to 

 the specimen prevents comparison of the bones in the orbital region, the zygo- 

 matic arch, and characters of the dentition. One can merely affirm that the teetli 

 were single-rooted, and probably of cylindrical form, that is, without the addi- 

 tional tubercle shown by the posteriorly situated teeth in Inia. In so far as these 

 latter may be said to recall something of the primitive condition of mokrs, 

 whereas Lophocetus is homodont, the dentition of the Miocene genus is more 

 specialized. But here we must not lose sight of the fact that Lophocetus is 

 adapted to a marine, and Inia to a fluviatile habitat. The utility of a homodont- 

 polyodont dentition to marine Carnivores, and the successive stages by which 

 this condition is attained among Cetaceans, have been clearly demonstrated by 

 Dames and others. 1 



In seeking for the nearest fossil allies of Lophocetus, attention is naturally 

 directed first toward those forms which are regarded as standing in the immediate 

 vicinity of Inia, possibly even in ancestral relations to the modern genus. Now 

 a number of Tertiary forms are known whose characters accord in the main with 

 those of Inia, and hence are properly included within the same subfamily. It 

 may be doubted whether any of them fulfil the requisites of a direct ancestor of 

 existing Iniinae, since they combine in their organization both generalized Cet- 

 acean characters, and also some others that indicate the animals were too 

 specialized to be the progenitors of Inia. Among these Tertiary forms that 

 present close structural resemblances to the modern type may be mentioned 

 Iniopsis, from the Caucasian Eocene, the skull of which is incompletely known ; 

 several Platanistid species which are grouped by Abel under the new generic 

 titles " Acrodelphis " and " Cyrtodelphis," from the European Miocene ; and 

 also the South American form described by Mr. Lydekker as Argyrocetus 

 patagonicus. We should expect to find no less intimate resemblances between 

 these forms and Lophocetus, on bringing them together. 



Before undertaking comparisons, however, a word or two is necessary to 

 explain the status and synonymy of the new names employed by Abel to 

 designate practically the same grouping of species as was formerly included 

 under Gervais's titles Champsodelplns and Schizodelphis. Both of these generic 

 titles were suppressed by the Viennese author 2 in his memoir of 1899, and the 

 names Acrodelphis and Cyrtodelphis substituted for them on the basis of newly 



1 Dames, W., Ueber Zeuglodon aus Aegypten. Pal. Abhandl., 1894, 5, p. 212. — 

 Fraas, E., Neue Zeuglodonten aus dem unteren Mitteleocan vom Mokattam bei 

 Cairo. Geol. und Palaeont. Abhandl., n. s., 1904, 6, p. 199-220. See also, concern- 

 ing origin of polyodont dentition among Squalodonts, Kiikenthal, W., Vergleich- 

 endanatomische und entwickelungsgeschihtliche Untersuchungen an Walthieren. 

 Denkschr. Med.-Nat. Gesellseh. Jena, 1893, 3, p. 421. — Weber, M., Studien iiber 

 Saugethiere. Jena, 1886, pt. 1, p. 194-195. 



2 Abel, O., Untersuchungen iiber die fossilen Platanistiden des Wiener 

 Beckens. Denkschr. k.k. Akad. Wissensch., 1900, 68, p. 840. 



