AiLEN. — American Collared Lemmings. 



EXPLANATION OF PLATE. 



Fig. 1-3. — Crown views of the two anterior cheek-teeth of the left side. 

 X 10.7. (In these ventral views, the Ungual side is at the left 

 hand, the external side at the right). 



Fig. 1. — Dicrostonyx hudsonius, M. C. Z. 8,671. 

 Fig. 2.— D. rubricaim, M. C. Z. 11,835. 

 Fig. 3.— D. groenlandicus, M. C. Z. 10,733. 

 Fig. 6. — Crown view of last lower molar of D. hvdsonius, M. C. Z. 4,167, 



right-hand side. X 10.7. , 



Fig. 8. — Crown view of last lower molar of D. ruhricatus, M. C. Z. 11,834, 



right-hand side. X 10.7. 

 Fig. 4, 5, 7, 9, 10. — Outlines of the interparietal and adjacent portion of 

 parietals and squamosals. X 5.9. 



Fig. 4. — D. hvdsonius, showing squamosals abutting against 



the interparietal, U. S. N. M. 190,377. 

 Fig. 5. — D. ruhricatus, with a prolongation of the parietals 

 separating the squamosals and interparietal, M. C. Z. 11,850. 

 Fig. 7. — D. richardsoni, interparietal broad with a bracket- 

 shaped anterior outline, U. S. Biol. Surv. 106,342. 

 Fig. 9. — D. exsul, interparietal squarish, M. C. Z. 11,885. 

 Fig. 10. — D. groenlandicus, interparietal somewhat lozenge- 

 shaped, M. C. Z. 10,733. 



