PROFESSOE FLOWER ON RISSO'S DOLPHIN. 19 



" Dents caduques ; deux paires a la partie terminale de la machoire inferieure 

 seulement, I), griseus." 



It now remains to be seen whether Fischer's opinion is strengthened or the reverse 

 by the new materials afforded by the two specimens described in the first part of this 

 communication. 



As has just been shown, the differences hitherto noticed between the supposed species 

 have resolved themselves into those of habitat, colour, and number of teeth. 



1. According to the previously observed habitats of the two species or varieties, the 

 present specimens should be referred to B. griseus, as all the examples of I), rissoanus 

 hitherto met with have been from the Mediterranean. 



2. According to the coloration, they should be B. rissoanus: but additional light is 

 thrown upon this part of the subject by these two specimens ; for they show conclusively 

 how extremely variable the species is in this respect. This might be inferred from the 

 absence of bilateral symmetry in the markings of each Ludividual, shown most strongly 

 in the adult example, where the markings were more profuse and complicated in cha- 

 racter. Laurillard speaks of the ground-colour of the females being of a " xmiform 

 brown," and therefore quite different from that of the two specimens now described. 

 Then, again, with reference to D. griseus, it must be remembered that the three descrip- 

 tions all differ somewhat as to the colouring, and, especially, that in the figure of the 

 type specimen from Brest numerous distinct irregular linear markings are indicated (as 

 previously mentioned). These with the general " grisatre " colour would appear to 

 show that it was more nearly allied in external characters to Risso's Mediterranean 

 Dolphin than to the black-and-white specimens described by D'Orbigny. If all the 

 specimens of alleged D. griseus had been uniform in colour, and all those of B. rissoanus 

 had presented another characteristic coloration, there would have been more grounds 

 for keeping them distinct ; but from the facts before us it is safer to conclude that we 

 have here an example, very rare among Mammals, of a species of variable and irregular 

 coloration. 



As to the teeth, the new specimens completely break down the specific distinction 

 previously drawn ; for, with the colouring of B. rissoanus, the adult one has the number 

 of teeth assigned to B. griseus, viz. ~ ; and that this is not the result of loss by age is 

 satisfactorily proved by the young individual, in which the teeth had not even cut the gum. 

 This last-named specimen was also extremely important, as presenting an undoubted 

 case of original unequal number on the two sides, viz. three and four, showing that the 

 exact number of teeth is a variable character ; and it also set at rest the question as to 

 whether the absence of teeth in the upper jaw is a congenital peculiarity, or arises, as 

 had generally been supposed, from their loss at an early age. 



It appears then necessary, until any better diagnostic characters are made out, to sink 

 the specific name of rissoanus in that of griseus, though it may be convenient to apply 

 the term "Eisso's Dolphin" to the peculiarly marked variety which was first made 



