10 lNTR0DUCT10^f. 



only the author's bare statement tliat the external characters of the 

 individaal whose skeleton is described were identical with those of a 

 previously-described species. 



In the case of species founded upon single skulls, absolute certainty 

 as to their distinctness can be reached only when large series of indi- 

 viduals known to be alike in their external and skeletal characters shall 

 havebeen acquired. When such series shall be at command, the limits 

 of specific variation can be determined with accuracy, and it will be pos- 

 sible to judge whether the characters held out as distinguishing the 

 species in question are really of specific value or only represent such 

 variations as are common among individuals of the same species. In 

 the mean time it is only possible in many cases to form opinions which 

 may or may not coincide with the truth. 



In this, as in all other families of animals, an arrangement of the 

 genera in a single linear series does violence to their natural aflinities, 

 while the attempt to introduce subfamily distinctions, with a view of 

 approximating the arrangement more closely to a natural sequence, is 

 here attended with great difficulties. Dr. Gill* has recognized four sub- 

 families: Pontoporibuc, Deli)hinapterina\ Belphiainw, aud GlohioccphaU- 

 na\ The genus Pontoporia {=Pontoporiince) T do not regard as belonging 

 to the DcJpn'niidae, ami shall, therefore, omit all further reference to it. 

 Tha GlohloceplidUnK {^^ Glob iccphalus and Grampus) are characterized as 

 having '' digits (second and third) segmented into numerous phalanges," 

 and to this are op[)osedthe Delpldnapterinca and Delphi ninw, which have 

 "digits (second and third) not segmented into more than 5-G phalanges 

 each." The facts do not appear to warrant this distinction, since Del- 

 pMiius delphis commoidy has from seven to nine phalanges in the sec- 

 ond digit, and Tnrsiops tursio and other species seven phalauges, which 

 figures also represent the number of phalanges in the second digit of 

 Grampus. 



The character which Dr. Gill employs for the separation of the Bel- 

 phinbuc from the BeJplunapterinw seems to me to be of much greater im- 

 portance. This relates to the condition of the cervical vertebrjc. In 

 Munodon and Delphinaptcrus {^Delphinapiterinw) the cervicals are all 

 distinct, while in the other genera of the family they are more or less 

 consolidated. I should be inclined, therefore, to unite Dr. Gill's Del- 

 fliininK and Glohiocephalince uuder the former name, and to oppose to 

 them the Belphinaptcrinai as a second subfamily. I am the more in- 

 clined toward the adoption of this division on account of having dis- 

 covered a character, which, in addition to that of the separate cervicals, 

 is common to Monodon and Pelphinapterus, but wanting in the other 

 genera. This is that in the narwhal and white whale the pterygoid 

 bones, instead of merely forming the walls of the posterior nares, extend 

 backward in the form of broad plates across the optic canal and articu- 

 late with the squamosals. 



*Gill. Arrangement of the Families of Mammals, 1872, p. 95. 



