1895.] 145 [Cope. 



Measurements. M. 



Diameters more anteriorly { "vertical 070 



t- transverse 06o 



Diameters near distal extremity \ ^^^ ^^'^ 



t. transverse 056 



For a length of 200 mm. from the anterior extremity the borders of the 

 gingivodental groove are sufficiently well preserved to demonstrate that 

 it was not closed. The edges posterior to this are more or less worn, so 

 that the roof might be supposed to have been broken away in the absence 

 of other evidence. This is, however, forthcoming, for the internal border 

 is so far preserved near the posterior extremity for a space of 135 mm. as 

 to show that no roof has existed. 



Omitting consideration of the generic characters, the following com- 

 parisons with other species may be made. In the TJUas moratus the gin- 

 givodental groove is deeper and narrower, and the inner edge is much 

 narrower. The external face is not so convex. The Siphonoeetus priscus 

 of Leidy resembles it more nearly in form, but the superior (external) 

 foramina are not so far inwards, and the two canals taken together con- 

 form nearly to the outline of the ramus in section, which is far from be- 

 ing the case in the TretuUas buccatus. There is no Meckelian groove. 

 In the Cetotherium palmatlanticam Leidy, the external face is not so con- 

 vex, and the internal gingival canals are, according to Leidy, "directed 

 upward and moderately forward." In the T. buccatus they are directed 

 forwards horizontally, and very little upwards. 



Dr. Leidy has regarded the presence of a Meckelian fissure on the 

 ramus of G. palceatlanticum as a speciflc character, and possibly as gen- 

 eric, as he has given a new generic name to it,* without diagnosis. This 

 fissure I have not observed in any of the rami described by me, except 

 in the case of the present species. It is figured by Van Beneden in some 

 of the Balnenidae of Antwerp, and is stated by him to be common to all 

 the Bahenidfe. It is, however, not visible in many recent skeletons, and 

 I am inclined to doubt whether it is normal in adult animals. When the 

 rami of recent Balaenidae dry, they sometimes split along the line of the 

 primitive Meckeliian groove, but not always. It remains to be seen 

 whether this is the origin of the fissure in the present species and in the 

 jaw described by Prof. Leidy. The generic name proposed by Prof. 

 Leidy (Protobalaena) is preoccupied by Van Beneden (1867). 



Cetotherium pusillum Cope, Amer. Naturalist, 1890, p. 616. 

 Eschrichtius piisillus Cope, Proceeds. Acad. Nat. Sci., Phila., 1868, p. 191 ; 

 1869, p. 11. 

 The fragment of the ramus of this species above referred to is longer 

 than any that have come under my observation, which now number five 

 individuals. Its length is 723 mm., and the diameters at a fracture near 



* Extinct Mamm. Dakota and Nebraska, 1869, p. 4i0. 



PKOC. AMER. PHILOS. SOC. XXXIV. 147. S. PRINTED JUNE 12, 1895. 



