76 bulletin: museum of comparative zoology. 



and Plate 4, figure 3 (two views), are both in the collection (Plate 2, 

 fio-ures 7 and 8). The peculiar form of the crowu of the former tooth 

 is due to the fact that the upper half has been restored in wax and not 

 properly shaped. The enamel is much rougher at the base than is in- 

 dicated in Gibbes's figure. The other tooth is at present much broken. 

 All the teeth, as Gibbes remarked, are hollow and filled with green 

 sand. 



None of the caudal vertebrae mentioned by Gibbes accompanied the 

 other bones. The small ones figured by him in 1847 in his Plate 2, 

 figures 4 and 5, might belong to the present species, but they are from 

 too near the end of the tail to present any very strongly marked char- 

 acters. They give a little support to the view that Dorudon serratus 

 is a form with relatively short vertebrae like Z. brachyspondylus minor, 

 instead of long vertebrae like B. cetoides. 



For the comparison of Dorudon with other American zeuglodonts, I 

 have had the use of the nearly complete skeletons of Basilosaurus cetoides 

 and Z. brachyspondylus minor, collected by Professor Charles Schuchert in 

 Alabama, and now in the National Museum, and a cast of the type skull 

 of Z. brachyspondylus minor Stromer, 1 in Teyler's Museum, in Haarlem, 

 which was sent to the National Museum for my use by the director, 

 Professor E. Dubois. 



The large species B. cetoides (or macrospondylus) is, I think, sufficiently 

 differentiated from the others by its excessively elongated lumbar verte- 

 brae and extremely thick epiphyses to be regarded as the representative of 

 a separate genus. Its scientific name is properly Basilosaurus cetoides 

 (Owen). Several Old World species have been associated with it under 

 the synonymic generic name Zeuglodon, but Z. isis Andrews is the only 

 one, apparently, which has elongated vertebrae. The dental formula of 

 Basilosaurus was not given by Miiller, and cannot be worked out fully 

 from the material in the National Museum. The formula for the lower 

 jaw, however, appears to be C. 3, I. 1, PM. 4, M. 3. The formula given 

 by Andrews for Zeuglodon is, i. § ; c. \ ; pm. % ; m ^, 2 but as this 

 is based on, or at least includes, species with short lumbar vertebrae, it 

 cannot be considered as necessarily correct for Basilosaurus, though the 

 difference, if any, will doubtless prove slight when the dentition of the 

 latter becomes fully known. 



In Basilosaurus cetoides the atlas is thick and the posterior articular 



i " Der Kleine Zeuglodon " of Miiller. 



2 A descriptive catalogue of the Tertiary Vertebrata of the Fayum, Egypt. 

 1906, p. 236. 



