A NEW FOSSIL PORPOISE FROM MARYLAND. 185 



causes the borders to be concave. The distal end is nearly transverse but 

 somewhat rounded, and is narrowly oval in section and tliinner than the distal 

 end of the radius. The proximal end is convex and is joined by a large, erect 

 lunate olecranon, unlike anything found in the recent delphinoids, and reminding 

 one rather of the ziphioids. The peculiar characteristics of the limb-bone^ above 

 described, when taken together, differentiate this species from any hitherto 

 known. 



The epiphyses of the humerus are detachable, the proximal one bring very 

 thick, and the distal one thin, especially on the radial side. 



Only one small, elliptical carpal bone has been preserved and none of the 

 phalanges. 



The dimensions of the bones of the pectoral limb are as follows: 



Humerus. — Total length, 67 mm.; greatest breadth at proximal end, 40; 

 greatest breadth at distal end, 30; greatest breadth across middle of shaft, 29; 

 diameter of head, 24; least thickness of shaft, 16; thickness at distal end, 18. 



Radius. — Length between centers of opposite extremities, 59; breadth at 

 proximal end, 24; breadth at distal end, 28; least breadth at middle, 18; thickness 

 at proximal end, 15; thickness at distal end, 12. 



Ulna. — Length, exclusive of olecranon, 58; breadth at proximal end, exclusive 

 of olecranon, 13; breadth at distal end, 24; least breadth of shaft, 12; thickness 

 at proximal end, 12; thickness at distal end, 10; length of olecranon, 23; breadth 

 of olecranon, 14; height of olecranon above proximal end of ulna, 15. 



Nomenclature. 



It is a matter of much difficulty to decide what name should be applied to 

 the specimen described in the foregoing pages. Numerous species of American 

 fossil cetaceans were based by Leidy, Cope and other authors on single teeth, a 

 vertebra or two, and the like, and unless one has material in hand which is stricth 

 comparable it is not easy to reach a conclusion as to whether the differences 

 observable are of specific importance, or due to age, individual variation, etc. 

 In looking over the type-specimens of American species, I have found one tooth 

 which shows a close similarity to those of the form herein described. This tooth 

 was from the Miocene of Virginia, and was described by Leidy in 1856, under the 

 name of Phoca wymani, which name Leidy in 1854 applied, without description, 

 to the fragment of a skull of a seal made known by Wyman in 1850, but not 

 named. In 1867, Cope added a description of three additional teeth from 

 Charles County, Maryland, under the name of Squalodon wymani, and also 

 described a second species, under the name of Squalodon mento, based on four 

 teeth from Charles County. In 1869, Leidy established the new genus Del- 

 phinodon for these two species and included them, with various squalodont and 

 zeuglodont forms, under the ordinal name of Zeuglodontes, but without assign- 

 ment to any family. Since that date the genus Delphinodon has been variously 



assigned to the Squalodontidae, Platanistidae, etc., but usually to the former 

 family. 



