G PROCEEDIISrGS OF THE NATIONAL. MUSEUM vol. 6b 



formed durino; each of these sedimentation intervals which shut off 

 a portion of the sea bed, and in consequence brackish water condi- 

 tions pi-evailed. Aquatic vegetation would thus gain a foothold and 

 airord favorable environmental conditions for sirenians. The occur- 

 rence of crocodiles {Thecachamysa?) and the soft-shelled turtle 

 {Trionyx) would also suggest that extensive lagoons were present 

 in the Chesapeake embayment. Only a few scattered bones of 

 sirenians have been found during the past 15 years, and this in turn 

 suggests that these mammals were far from being plentiful. In time 

 the barrier bars would advance landward and the lagoons would be 

 gradually filled up with sediments. Complete skeletons of the 

 smaller dolphins have been found above and below the zones which 

 contain shells of oysters. This shows that the ocean tides had free 

 access to these areas during such periods of sedimentation, and that 

 the bluish clay in which they were embedded was laid down in quiet 

 water some distance from land. The presence of certain river dol- 

 phin types related to Inm and Platanista tend to confirm the ex- 

 istence of a vast estuary in the present Chesapeake embayment. 

 Alni'^st all of the specimens of the larger cetaceans show either the 

 action of surf waves or the presence of strong currents; the parts of 

 the skeletons are widely scattered and associated vertebrae are of 

 rare occurrence. 



After a careful detailed study of the skulls of EurMnodelpMs in 

 the National Museum, I am unable to satisfy myself that any one of 

 them is identical specifically with any of the European species, 

 though it is not unlikely that such identity may be established later. 



Although there are a few more alveoli in the maxillae, these 

 skulls show a closer agreement with Eurhinodel'phis longirostris, the 

 smallest species known from the Antwerp Basin, than with any of 

 the others. The shape and relations of the anterior extremities of 

 the polatines, the depth and proportions of the braincase, the width 

 of the raised surface between the longitudinal furrows on the eden- 

 tulous portion of the rostrum, and the direction of the basicranial 

 axis are very similar. The differences pointed out in the descrip- 

 tions of these specimens seem to have sufficient weight to justify the 

 application of another specific name to the Calvert Miocene porpoise. 



Professor Abel's description ^- of the family Eurhinodelphidae 

 and its single genus Eurhinodelphis is as follows: 



Family EURHINODELPHIDAE 



Rostrum excessively elongated, occupying in one case {Eurhino- 

 delphis longirostris) nine-elevenths of the length of the skull; bones 

 of the rostrum very delicate ; premaxilla strongly attenuated, f orm- 



" Abel, O., Mem. Mus. roy. d'hist. nat. de* Belgique, Bruxelles, vol. 3, pp. 117-119, 

 1905. 



