﻿NO. 6 FOSSIL WHALEBONE WHALES TRUE 7 



off, but that the inner wall has remained further back than in 

 Ulias" (Op.cit.,p.27.) 



Metopocetus Cope. — " Metopocetus was established by Cope on 

 a much-damaged skull from the Miocene of North America. The 

 species is called M. durinasus. Cope himself thought that it might 

 be the same genus as Ulias and Tretnlias, which are known from the 

 lower jaw. The genus probably stands near Cetotherium (with 

 Plesiocetus) , but differs especially in that the nasals are short and 

 almost anchylosed together and with the f rontals. In addition, there 

 is a difference in the temporal crest, which, however, to judge by the 

 figure, is not distinct. The skull on which the genus is founded is 

 so much damaged that the relation of the frontals and nasals cannot 

 be clearly seen, and the length of the nasals cannot be correctly 

 guessed. If Cope was right in his opinion that the bones were 

 anchylosed, that would not be sufficient ground for establishing a 

 new genus. Anchylosis may result from advanced age, or from 

 pathologic conditions. Nearly anchylosed nasals are figured by Cope 

 himself in Cetotherium me goto phy sum. From the figure, which, 

 however, is only an outline of the skull seen from above, Metopocetus 

 agrees so well with Plesiocetus that a generic difference is not 

 probable." a ( Op. cit., pp. 27-28.) 



Cephalotropis Cope. — " Cephalotropis was established by Cope 

 from a very imperfect skull from the Miocene of North America. 

 The single species is C. coronatus. Cope himself thought that it 

 might be the same genus as Ulias or Tretulias. From Cetotherium 

 (with Plesiocetus) it is supposed to differ in having temporal ridges, 

 or angles, which are lacking in Cetotherium; but that is an error. 

 The anterior part of the temporal crest, that which is referred to, is 

 essentially the same in all extinct Finbacks. To judge from the 

 figure, there is no ground for separating Cephalotropis from Plesio- 

 cetus." (Op. cit., p. 28.) 



Rhegnopsis Cope.' — u Rhegnopsis was founded by Cope on a 

 fragment of a mandible from the Miocene of North America. On 

 the same piece Leidy established his Balana palceatlantica, which 

 later, without any further explanation, was transferred to a new 

 genus, Protobalcena. That generic name, however, was not valid, 

 as Cope pointed out, since it had already been used by Van Beneden in 

 another sense, and Cope adopted the name Rhegnopsis instead. The 

 only ground for the separation of Rhegnopsis from Cetotherium, or 

 other allied Finbacks, is the presence of a { Meckelian fissure/ a slit 

 which extends from the inner side of the jaw deep in through the 

 interior of the bone. In reference to the slit, Cope wrote in 1865 

 (p. 145) : ' I am inclined to doubt whether it is normal in adult 

 animals. When the rami of recent Balsenidse dry, they sometimes 

 split along the line of the primitive Meckelian groove, but not 



1 1 would remark as regards the nasals, which I have examined in the type- 

 specimen, that they are complete anteriorly as shown in Cope's figure, and 

 hence quite short. 



