Cope.] 14-4 fApril 5, 



This form is of much interest as representing in adult life a stage which 

 is transitional in typical Baltenidie. The alveolar groove is continuous 

 with the dental canal, and is permanently open. It is probable then that 

 this genus possessed teeth during a longer period than the existing Balse- 

 nidte, and that they were retained in place by a gum so long that the 

 canal could not close as is the case in the latter. The absence of the long 

 series of mental foramina characteristic of the true whales is further evi- 

 dence to this effect. 



Van Beneden, in his Descriptions des Ossemens Fossiles des Environs 

 d'Anvers, describes a Balienid under the name of Balcenula balcenopsis 

 which is represented by numerous individuals. I agree with Lydekker 

 (Catalogue of Fossil Mammalia in t/ie British Museum, Vol. v) that Van 

 Beneden has not given sufficient reason for separating the species gen- 

 erically from BahBna. There is also considerable diversity between indi- 

 viduals referred to the species. In a small specimen, a narrow alveolar 

 groove is present, but Van Beneden makes no reference to the cliaracter 

 in his description. As the groove is closed in large specimens figured, it 

 is possible that M. Van Beneden regarded the character as one of imma- 

 turity. This may be the case, as the groove figured by Van Beneden is a 

 very narrow one, and is quite different from the widely gaping channel 

 in the Ulias moratus, which is founded on an adult animal. 



Chai: specif. — This species is founded on a nearly entire right mandib- 

 ular ramus. The condyle and angle are wanting, as is also a piece from 

 tHe proximal part of the distal third of the length. This piece was found 

 with the rest of the specimen, but has been, for the present at least, mis- 

 laid. 



The ramus is moderately curved horizontally, but is not decurved ex- 

 cept towards the angle. A slight convexity of the inferior margin exists 

 at the anterior part of the proximal two-fifths of the length. The supe- 

 rior border is occupied with the widely open alveolar groove, which grad- 

 ually contracts in transverse diameter distally, so as to be closed for the 

 terminal fourth of the length. On this region two or three large foramina 

 issue from it on the middle line above, and the terminal mental foramen 

 issues at the superior extremity of the distal end, a little below the inter- 

 nal ridge on tlie external side of it. Of the borders of the alveolar groove 

 the internal is much lower than the external on the proximal sixth of the 

 length. The edges are then equal for a short distance, and are acute. 

 The internal then becomes the more elevated, and continues so until its 

 point of union with the external. The internal wall of the groove is at 

 first narrow, and its superior edge from being acute becomes narrowly 

 rounded, but becomes more obtuse distally as the wall becomes thicker. 

 The internal side of the ramus is very little convex. The external side of 

 the ramus is strongly convex in vertical section, hence it is that the exter- 

 nal edge of the groove becomes wider as it becomes lower, until at the be- 

 ginning of the distal third of the length it forms a plane distinct from the 

 convex external face. This external convexity growing rapidly less, the 



