212 DR. J. E. GRAY ON THE SKULLS OF DOLPHINS. [May 8, 



This lias been my universal experience : no sooner has a monograph 

 of a group of animals been put into print, than on the reexamination 

 of the group, you find it might have been improved. I have there- 

 fore sent to the Society the result of this reexamination and reconsi- 

 deration of the subject, and hope that it may facilitate the determi- 

 nation of the species of these little-known animals. I may add that, 

 from the experience I have had, I have no doubt that the skull 

 affords the best means of arranging the species into groups ; but I am 

 by no means sure that what I have considered a single species by the 

 study of the skull may not be found to be a group of several species 

 when we are able to examine the rest of the skeleton and the ex- 

 ternal coloration of the animals which have a skull of the characters 

 described. 



The genera of the Bottlenoses may be arranged according to the 

 skulls thus : — 



A. Beak of the skull elongate, compressed. Nasal triangle short. 



Symphysis of the lower jaiv elongate. 



Pontoporia. Beak of the skull high, compressed. Symphysis of 

 the lower jaw very long. 



Steno. Beak of the skull compressed, higher than broad. Sym- 

 physis of the lower jaw long. 



B. Beak of the skull elongate, depressed, broad, shelving on the 



sides. Nasal triangle short. Symphysis of the lower jaw 

 short, sloping. 



* Palate with a deep groove on each side behind. 



Delphinus. Beak elongate. Dorsal fin distinct. Teeth small, 

 slender. 



** Palate fat behind, without any lateral grooves. 



Clymene. Beak of skull elongate, depressed. Teeth small, slender. 

 Nasal triangle moderate. Dorsal fin distinct. 



Delphinaptertjs. Beak of skull elongate, depressed. Teeth 

 small, slender. Dorsal fin none. 



Tursio. Beak of the skull only rather longer than the brain-case, 

 conical, convex above, rounded. Teeth large. Skull high. 



Eutropia. Beak of the skull only rather longer than the brain-case. 

 Skull depressed. Teeth small. 



C. Beak of the skidl broad, flat above, edges slightly reflexed and 



bent up in front of the notch. Nasal triangle elongate. Sym- 

 physis of the loiverjaw short. 



Lagenorhynchus. Beak as long as or rather shorter than the 

 length of the brain-case. 



