6G BULLETIN 06, UNITED STATES NATIONAL MUSEUM. 



marginatum. The dorsal fiu is situated iiuicli farther back in P. margi- 

 natus than iu P, lateralis. 



The localities from which the difiereut specimens were derived are far 

 apart. 



On account of the i^resence of these differences, real or apparent, and 

 of others which may be perceived by comparison of the figures, it is not 

 X)0ssible to unite the species at the present time. 



Whj^ Cassin should have regarded Peale's species as belonging to 

 the genus Lagenorhynchus is not clear. The shape of the beak is cer- 

 tainly not characteristic of that genus. Since Prodelphinus is nob dis- 

 tinguishable from Belphinus by external characters in the present state 

 of knowledge, I have referred Peale's species to this genus with a mark 

 of interrogation. Its close resemblance to P. marginatum externally 

 is my chief reason for placing it here. 



PRODELPHINUS PLAGIODON Cope. 

 Ddpliinus pla<jio(lftn, Cope, Proc. Acad. Nat. Sci. Pliila., 1H6G, p. 29G. 



Complete data regarding three individuals belonging unquestionably 

 to this species are at command. The skeletons, photographs of the 

 exterior, certain of the viscera, and measurements of these specimens 

 are iu the collection of the National Museum. There is also a cast of 

 one individual. One specimen, No. :i2017, was captured off' Hatteras, 

 North Carolina, by the naturalist of the United States Fish Commission 

 steamer Albatross. The second specimen, No. 15030, was purchased by 

 the Smithsonian Institution from the fishermen of Pensacola, Fla.. 

 through Messrs. Warren &Stearnsofthatplace. A description of this in- 

 dividual has been given by the writer in the Smithsonian Report for 1884 

 (pt. 3, i)p. 317-321, Pis. i-vi). It is therein identified with P.plagiodon 

 (Cope), which species is iu turn regarded as apparently identical with 

 P. doris (Gray). While, after further reflection and comparison of speci- 

 mens, I am more than ever convinced of the correctness of the identifi- 

 cation of the freshly-acquired specimens with P. jj/a^fiofZow (Cope), on 

 the other hand I begin to doubt whether the latter species should be 

 regarded as identical with Gray's CUjmenia doris. If the relative pro- 

 l)ortions of the species alone are considered, the tn'O species do, indeed, 

 appear to be identical, but when the absolute size is regarded the matter 

 assumes a different aspect. The type skull of P. plagiodon is from a 

 youngish individual, yet it is larger than the type of P. doris or any of 

 the skulls called doris or duhius in the collections of the British Museum, 

 the Royal College of Surgeons, and the Museum d'Histoire naturelle, 

 The Pensacola and Hatteras specimens, which are clearly not old (the 

 epiph.\ses of the vertebral centra are not anchylosed), are still larger 

 than the type of P. plagiodon. They exceed the type of P. doris in lengtli 

 by 2.55 inches and 2.3 inches, respectively. The Pensacola skull is more 

 than an inch longer than the largest of the twenty-nine skulls of the 



