368 PROCEEDINGS OF THE ACADEMY OF [1896. 



and August, like adult, but darker, owing to greater abundance of 

 gray and tawny hairs and the leaden under-fur. Appearance of 

 young and old, at a distance, at all seasons, white. A pinch of hairs 

 from near middle back presents the following color pattern : short 

 under-fur very fine and silky white ; over-fur silky white with rarely 

 scattering black-pointed hairs and a few very long spinous hairs 

 with the basal two-thirds black, and the terminal one-third white 

 with a black tip. 



Winter pelage (No. 1,047, A. N. S., Phila. Port Foulke, Green- 

 laud) pure white throughout, except the black ear tij^s, which are 

 mixed with white hairs. Whiskers white. 



Cranial characters.— ToioX length of skull twice the greatest 

 breadth. Nasals narrow, compressed, their greatest breadth half 

 their greatest (diagonal) length. Superior premaxillaries barely 

 reaching bases of nasals. Supraorbital processes more greatly de- 

 veloped and widely flaring than in arcticus. Posterior interorbital 

 constriction narrow, its width considerably less than alveolar length 

 of upper molar series. Upper anterior incisors rooted on the max- 

 illaries nearly halfway from the inferior maxillo-preraaxillary sutures 

 to pm. 1 , the termini of roots lying within the inferior lateral plane of 

 the rostrum, but forming a marked interruption of the inferior ros- 

 tral profile, viewed laterally. Incisors slender, prolonged, deeper 

 than broad (transverse less than longitudinal diameter), the ante- 

 rior upper pair in adults, multistriate, the normal sulcus of inner 

 face, peculiar to all other members of the genus, being so filled with 

 a calcareous process as to obliterate the depression, the face of tlie 

 tooth presenting a more or less even, rounded and enamelled con- 

 tour, marked where the groove normally belongs by irreg- 

 ular longitudinal striae." With the skull, minus mandibles, resting 



''■'• I have submitted teeth oi (jrrvnlandicus to my friend Dr. J. C. Curry, a dentist 

 of Philadelphia, for examination of this character. He defines it in the fol- 

 lowing words : " The groove on the face of the tooth is filled with a grayish, 

 opaque, homogeneous substance, which, on first examination, would appear to 

 be continuous with the enamel. As it approaches the cutting edge its density 

 increases and it is more striated in appearance. A continued maceration of 

 the tooth, however, will enable the operator to separate this structure from 

 the enamel groove with a clear line of cleavage, and with care the part may 

 be removed entire. In the alveolus this structure is not contintious through- 

 out the length of the root, but seems to have its beginning in a little triangu- 

 lar flap, about one quarter of an inch from the entrance of the tooth pulp into 

 the base of the incisor. Like the tooth itself, this sulcus filling has a higher 

 per cent of inorganic matter as it approaches the cutting edge, varying from 

 about 40 per cent organic at base to 10 per cent at tip. At the incisive edge, 

 its composition seems more closely allied to that of the cementum of the osse- 



