30 EDWARD A. WILSON. 



There appears to 1)0 a good deal of individual variation in the extent and distri- 

 bution of the pigmentation in the hair of Stenorhinchus. The four skins in the 

 ' Discovery ' and ' Morning ' colleftion.s, although having in each case the main 

 distinctive character, are strikingly different in this respect. No. 66, for example, is 

 an exceedingly handsome skin, richly marked with jet Iduck and dark grey, particularly 

 upon the throat, shoulders, flanks and hind ilippers. These are the usual areas upon 

 which the dark markings appear, or, rather, one should say remain ; for the character 

 of the marking in all of the Antarctic seals is such that one may more easily consider 

 it brought about by the greater or lesser confluence of white spots upon a dark 

 ground. This is the case even in Lobodon, where the white spots are confluent to such 

 an extent that in many cases no trace of the ground colour is left. This is the case 

 also, and to a considerable extent, iu Stenorhinchus and Leptonychotes. It is less 

 apparent in Ommatophoca. The result of the partial confluence of white spots in 

 young examples of Lobodon, and iu all examples of Stenorhinchus, is that rings, more 

 or less complete, of pigmented hair remain to form the characteristic dappling on 

 certain areas, these being constant in each case. The first part of the body to be wholly 

 whitened is the abdomen and the throat, the last the Ijack and dorsal aspects of the 

 limbs and sides of the head. In No. 66 the pigmentation is much in excess of the 

 average, so that there are even black markings remaining on the abdomen, and the 

 throat is very richly marked. For descriptive purposes, the .skin of Stenorhinchus may 

 be conveniently divided into a dorsal, a ventral and an intermediate lateral area. The 

 first is dark grey with black markings, the second is pale with no marking as a 

 rule, the third is grey, freely spotted with both black and white. Specimen No. 65 

 is a richly marked skin, but of a different type to No. 66. The dorsal area is dark 

 grey but with multitudinous and small black markings, the lateral area freely spotted 

 with white and black, and the ventral area, particularly the throat, but slightly 

 marked with black. No. 18 is again a third type, with few and indistinct markings, 

 being of a rather dirty grey colour dorsally and ventrally, and only a pale grey below ; 

 yet there is no doubt, even iu this poorly-marked skin, that the distribution and 

 appearance of the darker markings is characteristic of Stenorhinchus. 



It is a significant fact that in the ten skulls of Stenorhinchus now in the British 

 Museum, there is to be found no variation at all in respect of the number, either of the 

 incisors or of the cheek teeth. In each case the formula is strictly Stenorhinchine, 



i.?zi2c,!^P.c.='-^ 



2—2 1—1 5—5. 



This uniformity in a species of the true seals is quite unusual. Lobodon car- 

 cinojjhagus, Phoca greenlandica, and Stenorhinchus leptonyx are the only species in 

 which I have been unable to discover aberrant dental formulae. This point is 

 obviously connected with efficiency from a functional point of view, for the teeth are 

 strong and well adapted to the food upon which their owners live, although they are 

 in each case also highly specialised in form. 



