INTRODUCTION. 1 1 



This arrangement of parts is not to be found in other genera of tlie 

 l)elpltinida\ but is cbaracteristic of the tluviatile dolphins {Plafanista, 

 etc.), to which indeed the DelpliinapterinK show m^wy marks of aftinity. 

 Their separate cervical vertebrie, prolonged pterygoids, broad pectorals, 

 and radimentary dorsal fin, taken together, entitle them, I believe, to be 

 regarded as a distinct subfamily. Elsewhere in the group I do not 

 perceive that broad divisions are called for. Professor Flower employs 

 provisionally the characters furnished by the shape of the head as a 

 means of dividing the family into two groups. These characters, as 

 Professor Flower himself admits, though useful and seemingly in accord- 

 ance with natural affinities, within certain limits, are not trenchant. 



The characters of the two divisions as regards the form of the head 

 are as follows:* 



a. With rouuded head, -without distinct rostrum or beak. (Among the genera in- 

 cluded here are CephaJorhynclms and Lagenorlnjnchus.) 

 h. Dolphins with distinctly elongated rostrum, or beak, generally marked off" from the 

 anteuarial adipose elevation by a V-shaped groove. (Comprises Ddiyliinns, 

 Tiirsiops, Prodclphinus, Steno, and Sofalia.) 



Leaving Monodon and Delj)Mnaptcrus out of consideration, this dis- 

 tinction is valid for the majority of the genera, but is broken down by 

 Lagcnorhynchns and Cephalorhynclius. In the former genus (included 

 in section a) the beak, though shorter than in Tursiops (included in 

 section ft), is quite distinct and well marked off from the forehead, while 

 in some species of Cephalorhynclius the head is certainly not "rounded'' 

 in the sense of being globose, but is conical. 



The second character of the sections has to do with the length of the 

 rostrum as compared with the total length of the skull. Here again 

 Lagcnorhynchus and Cephalorhynchus appear intermediate. CephaJo- 

 rhynchuH eutropia (section a) has the beak relatively as long as Tursiops 

 tursio (section b); the same is also true for some species of Lageno- 

 rhynchus. 



In spite of these considerations, however, I have employed these char- 

 acters in the artificial keys to the genera, given on pages 152 and 153, 

 believing them to be as useful, for that j)urpose at least, as anj^ which 

 can be formulated at present. 



Among the supergeneric distinctions employed by Professor Flower 

 isone which was brought into requisition for the firsttime and seems to 

 be of value; this relates to the position of the two pterygoid bones. 

 lu a number of genera these bones meet in the median line of the palate, 

 while in others they are widely separate. The value of this distinction 

 is, however, diminished by the fact that in some species of Lagcno- 

 rhynchus these bones are in contact, while in others they are widely 

 divergent; also by the fact that the two positions appear to occur in 

 some species, e.g., Sofalia gadamu, as an individual variation. Within 

 certain limitation, however, the character is apparently of much value. 



Characters and Divisions, pp. 504 and 511. 



