﻿NO. 6 FOSSIL WHALEBONE WHALES TRUE 5 



CETOTHERIUM Brandt. 1843 



Orbital plate of frontals, and parietals and frontals on vertex, as in 

 Plesiocetus. Posterior nasal extension, or process, of maxillae as in 

 Balcenoptera, but broader, more triangular, and less distinctly marked 

 off. Maxillae narrow. Premaxillae inserted between maxillae and 

 nasals proximally as in Balcenoptera; not expanded distally(?). 

 Nasals moderate. Tympanic bone rounded internally (that is, on 

 the edge nearest the median line of the skull). Alveolar groove and 

 dental canal as in Plesiocetus (f). Alveolar groove roofed. 



CEPHALQTROPIS Cope. 1896 



Differs from Plesiocetus only in having the apex of the supra- 

 occipital very rugose and deeply pitted. 



METOPOCETUS Cope. 1896 



Differs from Plesiocetus only in having the parietals on the vertex 

 rather shorter and the nasals also short. 



Genera based on mandibles 

 SIPHONOCETUS Cope. 1895 

 Alveolar groove and dental canal distinct. Groove roofed over 

 and perforate. 



Note. — I suspect that these characters are of no value and that Balcenoptera, 

 Aulocetus, Cetotherium, and Plesiocetus are all alike as regards the canal and 

 groove. 



ULIAS Cope. 1895 



" Alveolar groove and dental canal confluent in a gingivodental 

 canal." Canal open. No gingival canals. 



TRETULIAS Cope. 1895 

 Similar to Ulias, but with gingival canals at the sides of the 

 mandible. 



Winge's criticisms of Cope's genera 



Winge's comments on Cope's genera are appended. 



Siphonocetus Cope. — " To Cope's account [of this genus] two 

 objections have to be made. In the first place, it is certain that Cope's 

 interpretation of the canals in the lower jaw is incorrect. To con- 

 clude from his figures, representing diagrammatically a section of the 



