si>or j i;i> lioi.rniN. 



321 



Measurements of the skull of Prodelphinw dori . ' . J : the type of /'. plagiodon t 



So. 3684; and the type of 1'. d<»i>, British Museum, No 



Measurements. 



p. *,„-,. n,, T \!::;;:,'„'' e 



21915. U. S. 

 Nat Mus. 



U. s. 

 Nat Mas. 



cm. lOOths. 



lOOths. 



T.v],.' 



Bi • 



Mi, - . 



lout In. 



Total length 



Length <>t" beak 



Breadth «>t beak at base of notches 



Breadth of heal at Its middle 



Breadth <>t intermaxillariet at same point ' 



Greatest breadth between outer margins of iuter- 



maxiUariea, proxhnally | 



I t- ii :th of tooth-line 



Last tOOth to liase of maxillary notch 



Tip <>t beak to anterior margin superior nasal open 



ini: 



Tip of b.-ak to i ml of nest of pterygoid 



Breadth between orbital processes of frontal — 

 Breadth between binder margins of temporal fossaB. 



Length of temporal fossa 



Depi b of temporal fossa 



Total lengtb of mandible 



Depth between angle and coronoid process 



Height of crown of largest tooth 



Greatest diameter of crown at base 



Number of teeth 



100.0 

 58.2 



46.2 



26.9 



10.1 | 21.9 



5. 8 12. 6 



3. 3 7. 1 



43.1 



24.3 



9.1 



5.6 



2.8 



8. 1 17. 6 7. 8 ' 



23.6 51.1 , 21.0 

 5.3 11.5 ! 4.6 



82. 4 



34.7 



18.5 



14.4 



8.1 



5.6 



39.2 



7.3 



.8 



.5 



37-37 



33-34 



70.3 

 75. '1 

 40.1 

 31.3 

 17.6 

 12.1 

 85.2 



1 28.0 



100.0 



56. S 



21.2 



12.8 



6.5 



18.2 

 48.2 

 10.6 



65.9 



15.9 



18.0 

 14.2 

 8.1 

 6.1 

 36.7 

 7.1 



41.8 

 32.9 

 18.8 

 14.1 

 85.2 

 16.5 



35-35 

 34-35 



392 



23.4 



9.4 



4.9 



2.7 



7.3 



•JO. "J 

 4.0 



26.9 



28.7 



16.3 



13.1 



7.1 



5.3 



33.8 



6.0 



38-34 

 34-34 



100.0 



28. 



11.9 

 7.1 



18.8 

 51.8 

 10.4 



73.1 

 41.7 

 33.3 

 18.1 

 13.6 

 86.4 

 15.5 



TAXONOMY. 



The majority of species of Delphinidce are founded upon single skulls. 

 All dolphins' skulls differ from one another to a greater or less extent, 

 and it is impossible, therefore, to find any which will agree exactly with 

 the types. Furthermore, the limits of cranial variation have been deter- 

 mined only in the case of two or three well-known species. For these 

 reasons there is a strong temptation, when a fresh specimen of which 

 the external characters are undescribed is acquired, to erect a new spe- 

 cies. The skull presents differences which separate it from the type 

 skulls of any previously described species, and there is no criterion by 

 which one may judge whether these differences are of specific value or 

 onl} r represent individual variation. Such is especially the case in the 

 genus Prodelphinns, in which the species may be as few as three or four 

 or as many as twenty or tweuty-five. 



Under these circumstances there is no escape from a very unpleasant 

 dilemma. If a new species is erected, there is constantly a suspicion 

 that it is identical with some one previously described from the skull ; 

 while, on the other hand, if the newly acquired specimen is referred to 

 a species already in the literature, there is always the possibility that 

 if the external characters of the latter were known they would prove 

 the two to be distinct. It is seldom that cetologists have the oppor- 

 tunity to compare large numbers of individuals of the same species 

 in a fresh state, except in the case of such forms as Qlobiocqphalus, of 

 which large schools are frequently stranded. It is imperative that we 

 should make careful study of such material, and from the results of such 

 S. Mis. S3, pt. 2 21 



