b PROCEEDINGS OF THE ACADEMY OF 



Third Contribution to the Fauna of the Miocene Period of the ITnited States. 



BY EDWARD D. COPE. 



PLATANISTW^. 



A more than usually complete skeleton of Tretosphys grandajvus fur- 

 nishes some characters, whkh, taken in connection with others known to exist 

 in many others species of our Miocene dolphins, suggest that the true position 

 of all of the latter is in or near the family above named. 



In the skeleton mentioned there are preserved some twenty-four ribs, more 

 or less completely, and the anterior segment of the sternum. No pieces can 

 be referred as osseous hsmapophyses. The sternal piece also presents no pita 

 for articulation with such hfemapophyses, either anteriorly or posteriorly, 

 but rugose surfaces only. The probabilities are, therefore, that these elements 

 were cartilaginous, a feature which Flower considers to be characteristic of the 

 family Platanistida;. The ribs present the same type. The cnpiiulum and tubercle 

 are well developed to near the posterior part of the vertebral column, where 

 they become approximated, neither disappearing more than the other, la 

 the Physeteridae the tuhei'culum disappears posteriorly, while in the Delphin- 

 ida; the capilulum vanishes. In the Platanistidse both remain and become 

 united. 



The cranium of Lophocetus exhibits features of the same family. The 

 pterygoids are long, flat and extended anteriorly. The cavity which they roof 

 is long and narrow, not short and inflated as in the Delphinidse. The nasals 

 and frontals are elongate as in Pontoporia.* In another cranium of uncertain 

 reference, but probably of the same type, these elements are rather more short- 

 ened. 



The species referred to this family, which are so abundant in our miocene 

 beds, appear, so far as known, to have the cervical vertebrae, all distinct, and 

 generally much more elongate than in any recent forms. This peculiarity has 

 been observed in Priscodelphinus a tropins, and P. conradi, in Tretosphyg 

 grandaevus, as well as in several smaller species of the family. The only 

 cervical vertebra referable to those of Ixacanthus ca;lospondylus are 

 less elongate, and nearly as thin as some of those of Beluga canadensis; 

 the reference to that species is, however, quite uncertain. Of an even more 

 attenuated form is the cervical of Pontogeneus prisons Leidy, a Delphinoid 

 from the tertiary of Louisiana. 



The teeth of Tretosphys are known, and these show some afiinity to those of 

 Squalodon, in the striate enamel surface, and anterior and posterior edge sep- 

 arating the inner and outer faces. The fang is cylindric, the crown regularly 

 conic, the two together strongly curved. 



A cast of a tooth of Lophocetus calvertensis is quite similar in form to 

 the preceding, and small for the size of the animal. 



Such teeth belong, perhaps, to T. g r a n d aj v u s. The muzzle of a species 

 of similar size, also from Shiloh, N. J., is very long, narrow and depressed, the 

 intermaxillaries forming a broad obtuse elevation. The fragments of the muz- 

 zle of T. la c e rt s u s, and those of some of the Maryland Priscodelphini in- 

 dicate a similar form. Lophocetus Cope presents a somewhat similar form. 

 This genus (Proceed. A. N. Sci., 1867, p. 146) will perhaps be found to be 

 identical with one of the four which I have recognized through vertebral 

 characters among the miocene Dolphins ; but to which this reference is to be 

 made is not as yet certain. When the portions of crania at present in my pos- 

 session are carefully studied, this identification can no doubt be readily made. 



The compressed roots of the teeth of Rhabdosteus distinguish them from 

 those of the above genera, and constitute a point of resemblance to the exist- 

 ing Platanistidse. 



*A fine specimen of the cranium of this species from Montevideo is in the Museum 

 of the Academy. 



[March, 



