TRUE : THE FOSSIL CETACEAN, DORUDON SERRATUS. 67 



Cope in 1890 remarked: — "When the Z. bracJiyspondylus Miill. is 

 better known it may be found to be referable to a distinct genus, Doryo- 

 don Gibbes" (American Naturalist, 1890, Vol. 24, page 602). 



Dames in 1894 states that he cannot agree with Leidy in regarding 

 Zeuglodon bracJiyspo?idylus as a synonym of Dorudon serratus, and 

 affirms that the latter is easily distinguished from Z, bracJiyspondylus 

 or Z. macrospondylus (= Basilosaurus cetoides) by the form of the teeth. 1 

 His remarks on this point are as follows : — " The straight, high, and 

 pointed accessory cusps, which are very large as compared with the 

 principal cusp, suffice to distinguish the tooth-crowns of Dorudon serra- 

 tus from those of the Zeuglodons from Alabama ; in addition, the roots, 

 both branches of which are always nearly parallel in the latter, in Doru- 

 don diverge at an angle of about 80° . . . Whether one proceeds more 

 properly in keeping Zeuglodon and Dorudon separate as genera, or in 

 treating D. serratus as a separate species of Zeuglodon, is uncertain. I 

 should incline to the first course." 



In the following pages I shall endeavor to explain my own view, which 

 nearly coincides with that of Dames, and is that the genus Dorudon is 

 distinct from Basilosaurus, and that the species which Midler mentioned 

 as a small form of his bracJiyspondylus 2 is allied to the former but repre- 

 sents a distinct genus. 



It is somewhat remarkable that Gibbes did not mention more than 

 a part of the specimens which were sent me from the Museum of Com- 

 parative Zoology as belonging to the " Gibbes collection." One can only 



1 Pal. Abh., 1894, (2), Bd. 1, Heft 5, p. 16. He also corrects the erroneous 

 statement of Zittell (Handbuch Pal. Vert., 1893, p. 168) that Dorudon is based on 

 vertebrae of Z. brachyspondylus. 



2 The confusion between the large form of zeuglodont with short lumbar ver- 

 tebrae and the small form of zeuglodont with short lumbar vertebrae in Midler's 

 work is very puzzling. The latter is sometimes referred to by him merely as Z. 

 brachyspondylus, and sometimes as " der kleine Zeuglodon." He was in doubt as 

 to this small form, as shown by his remark on p. 29 : " Whether the small Zeuglo- 

 don is a separate species ... or the young of Zeuglodon brachyspondylus is still un- 

 certain at present." 



In the appendix to his work (p. 31), however, he describes the small skull now in 

 the Teyler Museum, Haarlem, as " a small individual of Zeuglodon brachyspondylus." 

 This would be satisfactory if it were not that he also describes the large, short 

 lumbar vertebrae on page 26 under the same name. 



Recognizing this difficulty, Von Stromer in 1903 (Mitth. Pal. und Geol. Inst. 

 Univ. Wien, 15, p. 85), limits the name brachyspondylus to the form represented 

 by large, short lumbars, and assigns the name brachyspondylus minor to the small 

 species with short lumbars. This nomenclature is accepted in the present paper. 



