36 SYSTEMATIC PALEONTOLOGY 



tion of the frontal and parietal bones on the superior walls of the skull. 

 They differ as follows : 



A temporal ridge; maxillaries little produced posteriorly; nasals not 

 produced beyond frontal, coossified with the frontal and with each 

 other Metopocetus Cope. 



A temporal ridge; maxillaries much produced posteriorly; nasals free from 

 f rentals and from each other, produced well anteriorly. CepTiaZo^ropis Cope. 



No temporal ridge; maxillaries much produced posteriorly; .nasals free from 



frontals and from each other, well produced forwards Cetotheriuvi 



Brandt. 



" The specimen on which the genus Metopocetus is founded is quite 

 mature, so that the sutures are coossified. The frontomaxillary and 

 frontopremaxillary sutures are, however, distinct, as they appear to me, 

 and they are remarkable for their position. They extend but little 

 posterior to the external narial openings. The latter are, in relation 

 to the supraoccipital crest, anterior, but in relation to the position of 

 the nasals, posterior. The nasals are short for a Balsenid, although 

 they enter wedge-like into the frontals for a considerable distance. 



" The position of the genera Metopocetus and Cephalotropis may be 

 similar to that of the genera Ulias and Tretulias, which are known from 

 mandibular rami only. One or both of the former may be identical with 

 one or both of the latter ; but of this there is as yet no evidence." Cope, 

 1896. 



Metopocetus dukinasus Cope. 



Plate XVIII, Figs. 1, 2a, 2b. 



Metopocetus durinasics Cope, 1896, Free. Amer. Philos. Soc, vol. xxxv, p. 141, pi. 

 xi, fig. 3. 



Description. — " The specimen which represents the Metopocetus duri- 

 nasus is a cranium posterior to the nares, lacking the left exoccipital and 

 squamosal regions, and the right zygomatic process. Both occipital 

 condyles are preserved, and the basicranial region as far as the anterior 

 nares. 



"The supraoccipital extends well forwards and its lateral crests 

 present a moderate concavity outwards and forwards. Its apex is 

 represented by a semicircular mass, posterior to which it is deeply con- 

 cave, and the concavity is divided by a longitudinal median crest. The 



