Troxell — Rodents of Genus Iscliyromys. 125 



row M 2 and by the general absence of secondary tubercles, 

 external basal cusps, etc. In the ratios given in the table 

 beyond, it is seen that I. pliacus is over 50 per cent larger 

 in certain dimensions and averages about 30 per cent 

 greater. 



Fig. 2 Fig. 3 



Fig. 2. — Iscliyromys typus nanus, subsp. nov. Holotype. Cat. No. 12519, 

 Y. P. M. Three molars from right lower jaw. M 1 - 2 very narrow. X 2. 



Fig. 3. — Iscliyromys typus nanus, subsp. no v. Paratope. Cat. No. 12555, 

 Y. P. M. Left lower molars, to show results of wear. X 2. 



Iscliyromys typus lloydi, subsp. nov. 



(Figs. 4, 5, 7.) 

 Holotype, Cat. No. 12521, Y. P. M. Oligocene (lower Oreodon beds), 

 from the ranch of Mr. Paul Zerbst, 10 miles north of Harrison, Nebraska. 



This new subspecies is based upon an unusually com- 

 plete skull and jaws, together with certain portions of the 

 skeleton. These were found in 1915 by the writer who 

 takes pleasure in adding them to the collections of Pea- 

 body Museum. The new name is given in honor of Dean 

 Lloyd of the University of Michigan, in appreciation of a 

 delightful friendship. 



Fig. 4. — Iscliyromys typus lloydi, subsp. nov. Holotype. Cat. No. 12521, 

 Y. P. M. X 2. A, molars and premolar of lower right side, and single 

 deciduous premolar, Dp 4 , from opposite side. B, left upper molars and pre- 

 molars; the latter were drawn from a vertical position, and the skull was 

 then rotated inward in order to get the crown view of the molars. 



The specimen is moderate in size and corresponds in 

 general to the dimensions of I. typus Leidy. The upper 

 molars, unlike those in most specimens, do not decrease in 

 size toward the rear, for the last molar is actually greater 

 than the premolar or M 1 . The third permanent premolar, 

 the first of the cheek series, is just coming into view ; it 

 was actually hidden beneath the conical deciduous prede- 

 cessor when first worked out of the matrix. A single 

 tubercle with a crescentic ridge on the postero-internal 



