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Show 470 PROF. FLOWER ON THE DELPHINIDJE. [Nov. 20, epiphyses 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 circumstance 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 this important question, owing chiefly to the difficulty of obtaining a sufficient number of adult specimens of which the sexes are known. Fischer1 has, however, recently published some extremely interesting observations upon the sexual differences of the skulls of two of the species most frequently met with on the French coast, differences which will probably be also found in other members of the group. In Delphinus 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 hones 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 Delphinus tursio corresponding differences were observed. In the males the rostrum is longer and relatively narrower ; the intermaxillaries aremore prominent and convex, especially in their posterior half; 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 external 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 differences 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 numerous, they become extremely small at the ends of the series, particularly in front, and are often lost or concealed in the gum. And when circumstances 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. 1 " Cetact'8 du Sud-Ouest de la France " (Actes de la Society Linneenne de Bordeaux, t. xxxv. 1881). |