472 



PROF. FLOWER ON THE DELPHINID^. [NoV. 20, 



In the same memoir are also valuable observations upon the differ- 

 ences observed in the number of the vertebrae and ribs, as well as in 

 the external coloration of different individuals, which deserve careful 

 consideration, and as opportunities occur further development and 

 corroboration. 



Besides the usual distinctive characters derived from the length 

 and form of the rostrum and the number and size of the teeth, the 

 condition of the pterygoid bones, though hitherto much neglected, 

 seems to me one of great importance in separating the different 



Fig. 3. Palate of I)el2Mnapterus leucas. The pterjgoid bones are widely 

 separated in the middle line, and of comparatively simple form, the air-sinus 

 between their laminjB being very little developed. 



groups of Dolphins. The remarkable involution of this bone, by which 

 it encloses a large air-sinus opening behind between the outer and inner 

 laminae (see fig. 1), is peculiar to the family Delphinidce, and is pos- 

 sessed by all its members. Sometimes, in what may be considered the 

 most typical forms (as in Delphinus as now restricted (fig. 9), Tursio 

 (fig. 5), Steno (fig. 6), &c.), the bones are large, and come into 

 apposition in the middle line by straight surfaces of considerable 

 extent. In others, as Phoccena (fig. 2), Monodon, Delphinapterus 

 (fig. 3), they are small and widely separated, having the posterior 

 apex of the palatine bones wedged in between them in front and a 



