Cope.] 1^4: [Aprils, 



tardation. Or, second, it may have been derived from Ulias or its ances- 

 tor, by development of the roof about the gingival canals only, leaving 

 the remainder of the groove open. In the latter case it represents a stage 

 intermediate between Ulias and Cetotherium. But one species is known 

 to me. 



Ckar. specif. — This species is represented by parts of the mandibular 

 rami of two individuals, both preserved in the Museum of Johns Hop- 

 kins University of Baltimore. One of these measures 607 mm. in lengtli, 

 and is in fairly good preservation ; the other is a shorter fragment, and is 

 considerably worn. They agree in all respects. 



The longer fragment is gently curved both inwards and downwards. 

 It is compressed anteriorly, and more depressed posteriorly, so as to be 

 but little deeper than wide. The external face is very convex, more so 

 posteriorly than anteriorly, so that that part of the superior wall which is 

 developed is horizontal, as in the Siphonocetus priscus Leidy. The internal 

 face is little convex, and is slightly concave on a line near to and parallel 

 to the inferior border. Generally this angle is obtuse, and is a little more 

 than right ; anteriorly, near the extremity it becomes more ridge-like. 

 Posteriorly the section of the ramus represents more than a half-circle, 

 the base being the internal face. The internal basal concavity referred to 

 disappears posteriorly, but its place is occupied by a Meckelian fissure, 

 which extends along the bottom of the groove, disappearing at the end of 

 the terminal two-fifths of the length. 



The gingival canals are very oblique, extending horizontally forwards 

 and outwards. The internal foramina issue at spaces of one and two 

 inches, and they are not connected by a superficial groove. The superior 

 (external) series are equally oblique, extending forwards and opening 

 obliquely upwards. Only two of these canals are present on the speci- 

 men, and these are on the posterior two-fifths of the length. They are 

 not complete on the external side, and are therefore only grooves. The 

 common canal is open external to them, and separates the superior from 

 the external face of the ramus. It has not the form of the section of the 

 ramus as in other species, but is shallow, and with its long axis oblique 

 to that of the section, and parallel to that of the superior oblique part of 

 the external face. It is shallower than in the Ulias moratus, and the 

 species of Cetotherium, and is separated by a wide osseous space from the 

 inferior border. That tliis form is descended from one with a larger canal 

 is indicated by the fact that the fractures of the ramus display a closed 

 fissure extending from the floor of the canal vertically downwards. The 

 canal is overhung on the inner side by a narrow free border of the supe- 

 rior perforate wall. 



Measurements. 



M. 



Length of fragment 607 



Diameters posteriorly { ^"tical 077 



t. transverse 078 



