470 PROF. FLOWKR ON THE DELPHINID^. [NoV. 20, 



ej)ipliyses are all free on the vertebrae and the bones of the limbs, 

 and of which the carpus is but very imperfectly ossified. Want of 

 appreciation of this circnmstance has led to many errors in the 

 discrimination of the species of this group. 



Sex also appears to exercise an important influence upon the 

 form of the skull, although very little attention has hitherto been 

 paid to tliis important question, owing chiefly to the difficulty of 

 obtaining a sufficient number of adult specimens of which the sexes 

 are known. Fischer ' has, however, recently published some ex- 

 tremely interesting observations upon the sexual differences of the 

 skulls of two of the species most frequently met with on the French 

 coast, diff'erences which will probably be also found in other members 

 of the group. In Belphinus delphis he found that in the male the 

 rostrum is more elongated, more regularly tapering forwards, and less 

 dilated in its middle portion. The external borders of the intermaxil- 

 laries are subparallel to the corresponding borders of the maxillaries. 

 The crests of the cranial bones are more elevated, the temporal 

 fossa more ovoid, and the whole cranium rather higher. In the 

 females the rostrum has a more triangular form, the triangle of 

 the intermaxillaries is more dilated at its base, the apex of the 

 rostrum is less slender, the temporal fossa is broad and rounded. 



In Belphinus tursio correspondingdift'erences were observed. In the 

 males the rostrum is longer and relatively narrower ; the intermaxil- 

 laries aremore prominent and convex, especially in theirposteriorhalf ; 

 in this region the external border of the maxillaries is almost parallel 

 to the corresponding portion of the intermaxillaries ; the crests of 

 the cranium are more elevated, and less sloping laterally. The heads 

 of the females are remarkable for the breadth of the rostrum at its 

 base and its middle part ; the rostrum consequently has a more 

 triangular form ; the intermaxillaries are more flattened ; the ex- 

 ternal border of the posterior portion of the maxillaries is not parallel 

 to the external border of the intermaxillaries, but it has a rounded 

 projection outwards. The cranium of the female is relatively a 

 little broader than that of the male ; its height is the same in the 

 two sexes. The mandible is a little more elongated in the male. 



Such diff'erences as these are, it will be observed, quite as great 

 as many upon which Dr. Gray has founded distinct species. 



No dependence can be placed upon the exact number of the teeth 

 in discriminating species. In the first place there is often a great 

 difficulty in counting the teeth of the skulls met with in museums, 

 as, especially in those species in which they are nimierous, they 

 become extremely small at the ends of the series, particularly in 

 front, and are often lost or concealed in the gum. And when cir- 

 cumstances permit of their exact enumeration, variations in number 

 are often met with, even in different sides of the same jaw. The 

 range within which the numbers may vary in a single species has 

 been recorded by Fischer, in the memoir cited above, in Delphinus 

 delphis, and will be referred to again when speaking of that species. 



' " C6tact8 du Sud-Ouest de la France " (Actes de la Societe Liiincenne de 

 Bordeaux, t. sxxv. 1881). 



