Cope.] 14:0 [April 5, 



llie later genera. In Cetolherium and in later Balixjuldse tbe groove and 

 canal are fused, the gingival roof is complete, and it is perforated. It 

 would appear, then, that Ulias may be descended from the undiscovered 

 genus above mentioned, while Tretulias is descended from Siphonocetus. 

 The exclusively Neocene genera may be tabulated as follows : 



I. Alveolar groove and dental canal distinct. 



Alveolar groove open Not discovered. 



Alveolar groove roofed over and perforate Siphonocetus Cope, 



II. Alveolar groove and dental groove confluent in a giugivodental 

 canal. 



Gingivodental canal open ; no gingival canals Ulia^ Cope. 



Canal open ; gingival canals at one side Tretulias Cope. 



Canal with complete and perforate roof. Cetotheriam Brandt. 



SiPHONOCKTUS PRisccs Leidy, gen. nov. Balaena prisea Leidj^ Pro- 

 ceeds. Academy Pldlada., 1854, p 308. Eschrichtius priscus Leidy, 

 Cope, Proceeds. Acad. Philada., 1869, 11. Leidy, Extinct Mamm. 

 Dakota and Nebraska, 1869, p. 441. Infra Plate vi. Fig. 8. 

 Specimen in Museum of Academy of Natural Sciences of Philadelphia. 



Siphonocetus expansus Cope. E&chric7iiius expansus Cope, Proceeds. 

 Acad. Philada., 1869, p. 11. 

 The two mandibular rami ascribed to this species are the property of the 

 Maryland Academy of Sciences. The collection of Johns Hopkins Uni- 

 versity contains a fragment of a ramus of an individual of rather smaller 

 size than the types. Plate vi. Fig. 5. 



Siphonocetus clabkiancs Cope, sp. nov. Plate vi, Fig. 4. 



In the collection of the Johns Hopkins University there are portions of 

 mandibular rami of two species of Siphonocetus. The cranium of this 

 genus is unknown, but it is probably similar in character to that of the 

 Cetotheiium of Brandt. This genus differs from Balsenoptera in having 

 the elements between the supraoccipital and the nasals much elongated, 

 so that there is a sagittal crest of greater or less lenglh, and in the non- 

 union of the dia- and parapophyses into a vertebral canal,* in which it 

 agrees with Eschrichtius of Gray. Some of the rami described belong 

 possibly to species of Balajnoptera, and it remains for future discoveries 

 to ascertain which these are. 



One of the species above referred to is the Siphonocetus expansus Cope.f 

 The other species differs from all of those known to me. In dimensions 

 it exceeds those of any of the species described in this paper, and is only 

 exceeded by the species which I have described (I. c.) under the names 



*See American Naturcdist, 1890, p. 611, where these genera are characterized ; but Van 

 Beuedeu's name, Plesiocetus, is used for Cetotherium, and the latter name for Eschrich- 

 tius of Gray. 



t Proceeds. Academy Philada., 1869, p. 11. 



