■14-1 Berry and Gregory — Prorosmarus alleni. 



Art. XL. — Prorosmarus alleni, a new genus and species 

 of Walrus from the Tipper Miocene of Yorlioicn, Vir- 

 ginia ; by Edward W. Berry and William K. Gregory. 



During a recent excursion of one of the classes in geology 

 of the Johns Hopkins University, one of the students, William 

 E. Curley, Jr., found on the beach at Yorktown, Va.,* a left 

 mandibular ramus of a new extinct mammal evidently allied 

 to, but much more generalized than the existing species of 

 walrus, Odobamus rosmarus and Odobcenus obesus. The 

 specimen was presented to the Department of Geology of the 

 University, where it is now deposited under the care of 

 Professor William Bullock Clark, who has generously entrusted 

 it to the present writers for identification and description. 



The new genus agrees with Odobamus : (1) in the general 

 characters of the mandible; (2) in the general location of the 

 mental foramen, which is in each case followed by a much 

 smaller foramen ; (3) in the cylindrical shape of the cheek 

 teeth. In other characters Prorosmarus is much more 

 primitive and approaches the Otariidse or Eared Seals in the 

 following features : (1) The mature jaw retains two well devel- 

 oped incisors in each ramus as in the young walrus, the adult 

 walrus lacking the incisors. (2) The canine retains its primi- 

 tive position and caniniform shape, whereas in the walrus the 

 canine has been taken over into the molariform series, as 

 shown by its biting against the molariform outer upper incisor 

 and by its separation from the molariform series in the young- 

 jaw. The interpretation of this tooth as a canine in Odobamus 

 was adopted by Flower, Huxley, and J. A. Allenf in the solu- 

 tion of the long vexed question of the homologies of the 

 unique dentition of the walrus. (3) The inner side of the 

 lower canine of our specimen is considerably worn, and hence 

 to judge from the conditions in other Pinnipeds the upper jaw 

 must have retained three functional incisors in the adult. 

 (4) Viewed from the side the whole ramus is less curved 

 downward and the chin and symphysial surface is much more 

 slender and slopes more forward than in Odobamus, but is 

 much heavier and more roundly developed than in the Otaries. 

 The posterior half of the ramus is thus relatively deeper 

 and the anterior half is relatively shallower than in Odo- 

 bamus. (5) The opposite symphysial surfaces did not be- 



* These late Tertiary littoral deposits have been recently recognized by 

 Clark and Miller as distinct from the nnderlying beds and formally named 

 the Yorktown formation. 



f See summary in Allen's "History of North American Pinnipeds." 

 Washington, 1880, pp. 47-57. 



