1883] PROF. FLOWER ON THE DELPHINID^. 469 



study of the characters of the known species the materials at present 

 available are very insufficient, and doubtless there are many species still 

 to be discovered. I trust, however, that something will have been 

 done to clear the way for future work ; at all events I have avoided 

 adding to the existing confusion by introducing a single new name. 

 It seems to be the rule with some zoologists to assume that any 

 newly found individual, especially if in a new locality, belongs to a 

 new species, to name it, and to leave for others to prove its identity 

 with already described forms. The opposite view, that a species 

 should not be considered distinct imless some definable and tan- 

 gible character can be shown in which it differs from others, appears 

 to me to be preferable, and therefore, following Prof. Van Beneden, 

 the highest living authority on the Cetacea, I have abandoned the 

 old assum])tion, upon which so many new species were founded, 

 which limited the geographical area of each species to a small and 

 circumscribed portion of the ocean, and placed imaginary barriers to 

 its distribution where none really existed. 



Species founded upon osteological characters alone are, of course, 

 not of the same value as those based upon a full knowledge of the 

 external characters, habits, &c. Probably many sections which among 

 other groiips of animals we should call distinct species are united by 

 this method ; but still, when the only certain information we possess 

 of their structure is derived from their bones, as in the case of so many 

 Cetaceans, no other course can be followed. It is, however, not so 

 much to specific distinctions that this research has been directed, as 

 to discover the mutual relations of the different modifications of the 

 Dolphin type to one another, and their association into groups which 

 may be considered (following the custom adopted in the arrangement 

 of other groups) of generic value. 



It will be necessary to precede the examination of the special 

 groups by some preliminary observations applicable to all, upon 

 variations of form depending upon age, sex, and individual peculiarity, 

 the study of which has been hitherto too much neglected, and of 

 which our knowledge is unfortunately still imperfect. 



In all Dolphins the form of the skull alters considerably with age, 

 the rostrum or beak becomes larger in older animals, being both 

 longer and wider in proportion to the brain-case. The teeth become 

 actually larger, in consequence of a more considerable portion of the 

 broad base of the crown rising out of the alveolus as the slender 

 apex wears away, and they become more distant from each other 

 through the growth of the maxillary bones. 



Thus the proportions of length and width of beak, and number 

 of teeth in a given space (so much used by Gray to distinguish 

 species) cannot be relied upon, except in comparing perfecth/ adulf. 

 animals ; and when the skull alone is jjresent, it is extremely difficult, 

 if not impossible, to tell the relative age of the individual, as, con- 

 trary to what takes place in many other mammals, the sutures of 

 the cranium close very early in Dolphins. Even of the basilar suture, 

 wliich in Seals for instance is only united in old age, no traces 

 are left in Dolphins about three-quarters grown, and in which the 



