_Mustela cicognanii angustidens_, Hay, Iowa Geol. Surv. Bull., 23:32, 1914; Hay, Carnegie Inst. Washington, Pub. no. 322A:252, October 15, 1924; Hay, _ibid_., Pub. no. 390 (vol. 2): 528, 1930; Hall, _ibid_., Pub. no. 473:111, 112, November 20, 1936: _Type._--Female, adult, skull and lower jaws lacking zygomata, right P2 and incisors, no. 12432, Amer. Mus. Nat. Hist.; from Conard Fissure, four miles west of Willcockson, Newton County, Arkansas; obtained sometime in the period 1903 to 1905 inclusive (see plates 8, 14). _Range._--Known only from the Pleistocene deposit in Conard Fissure, at the type locality in northern Arkansas. _Description._--_Skull._--Male (based on nos. 12437, 12441 and 12444): See measurements and plates 7 and 8; weight, unknown; basilar length, 38:1 (36:6-39:2); length of tooth-rows more than length of tympanic bulla; breadth of rostrum measured across lacrimal processes less than a third of basilar length; interorbital breadth ordinarily equal to distance between glenoid fossa and posterior border of external auditory meatus; zygomatic breadth probably averaging approximately the same as distance between last upper molar and jugular foramen. Female (based on nos. 11766 and 12435): See measurements and plates 8, 12-14; weight, unknown; basilar length, 34:0 (32:5-35:1); length of tooth-rows more than length of tympanic bulla; breadth of rostrum about equal to (more or less than) 30 per cent of basilar length; interorbital breadth less than distance between glenoid fossa and posterior border of external auditory meatus; zygomatic breadth probably less than distance between last upper molar and jugular foramen. Comparison of the cranial description given above with those of the American races of _erminea_ from the far north will show that many characters are held in common--more than with more southern subspecies of _erminea_. _Remarks._--The ten specimens studied by the writer fall into two groups of six larger individuals and four smaller. Upon comparing these with each sex of the three species of American Recent weasels, _frenata_, _erminea_ and _rixosa_, it is seen that size, and to some degree shape, rule out of consideration both sexes of _rixosa_ and also males of _frenata_. Thus we are left with females of _frenata_ and males and females of _erminea_. So far as size is concerned, it can be assumed that the larger specimens are females of _frenata_ and that the smaller are males of _erminea_. This assumption has in its favor also, the fact that the postglenoidal length of the skull accords with that in Recent specimens. The difference in this regard in Recent animals is that the postglenoidal length of the skull, expressed as a percentage of the total (condylobasal) length of the skull, amounts to: