54 BULLETIN 73, UNITED STATES NATIONAL, MUSEUM. 



SEX CHARACTERS. 



It will be found from an examination of the foregoing descriptions that in those 

 specimens in which the sex is known to be female, or is marked as such, the pre- 

 maxillsB are comparatively narrow, the mesirostral ossification only slightly devel- 

 oped, the prenarial basin undeveloped, and the teeth quite slender, with a diameter 

 of from 10 to 14 mm. As the teeth in some of them have closed roots there can be 

 no doubt that they are adults. On the other hand, those skulls known or believed 

 to be from adult males have the mesirostral ossification enormously developed, 

 a deej) prenarial basin, and fusiform teeth with closed roots and a diameter of from 

 25 to 30 mm. It appears to be a fact, therefore, that in the females the mesirostral 

 ossification is never greatly developed at any age, that the teeth are never thick and 

 fusiform, and that the prenarial region is never deeply concave. Immature indi- 

 viduals present, of course, the appearance of the females, except that the teeth 

 are open at the root and that the mesirostral ossification is not developed at all. 

 Conversely, the females, broadly speaking, always present characters of immaturity, 

 but in adults the roots of the teeth arc, of course, closed. 



That these conclusions are correct is borne out by an examination of descrip- 

 tions and figures of specimens from other parts of the world, for which purpose 

 a few are available in the writings of New Zealand zoologists and others. Hector, 

 for example, in 1873," published a description and figures of a skull from the Chat- 

 ham Islands which had a large mesirostral ossification, deep prenarial concavity, 

 and large, thick teeth, having a diameter of 34 mm. Tiiis is the same combination 

 of characters found in the Newport specimen, which is known to be a male, and the 

 Bering Island skulls supposed to be those of males.*" 



In 1876,'^ Ilaast figured and described a female 2G feet long, and hence pre- 

 sumably adult, from Lyttleton Harbor, New Zealand, which had a small develop- 

 ment only of the mesirostral ossification, a slight prenarial depression, and rather 

 slender teeth with closed roots and a diameter of 19 mm. This combination of 

 characters is found in the Barnegat skull, also known to be an adult female. 



In the same paper Haast describes '^ and figures the skull of another female 

 from Akaroa Harbor, New Zealand. This individual was larger than the last and 

 was accompanied by a suckling calf. Hence, there can be no doubt that it was 

 mature. The skull shows a moderate development of the mesirostral ossification, 

 and slender cylindrical teeth with closed roots and a diameter of 16 mm. 



It is demonstrated from the foregoing discussion, I think, that the sexes can be 

 distinguished by the skulls, when adult, or by the teeth alone. 



Reverting now to ZvpMus gervaisii, which was mentioned on p. 30 as perhaps 

 constituting a separate species, it will be seen by examining the figures given by 



o Trans. New Zealand Inst., vol. 5, 1873, p. 1G4, pis. 4-5. 



b Hector also figures a tooth from a specimen found at Manawatu beach in pi. 5, fig. 3, which is like 

 those of the Chatham Island specimen in size and shape (diameter 34 mm.), and should belong to a male, 

 but as he does not figure or describe the skull this can not be used in the present discussion. 



cTrans. New Zealand Inst., vol. 9, 187G, p. 430, pi. 24, figs. A and c; pi. 26, fig. 4. 



dldem, p. 440, pi. 24, fig. b; pi. 2G, fig. 3. 



