26. _M. (Pitymys) fatioi_, 67103, Zermatt, Switzerland, immature.
27. _M. (Pitymys) pinetorum_, 76834, 2 mi. N Baldwin, Douglas Co., Kansas.
28. _M. (Pitymys) pinetorum_, 68545, 1 mi. NE Pleasant Grove, Kansas.
29. _M. (Pitymys) quasiator_, 30709, Teocelo, Veracruz, (_d_) ventral view.
30. _M. (Pitymys) quasiator_, 19878, 5 km. N Jalapa, Veracruz.
31. _M. (Pedomys) ochrogaster_, 75036, 1 mi. N, 2 mi. E Oberlin, Kansas.
32. _M. (Stenocranius) miurus_, 51152, Lake Schrader, Brooks Range, Alaska.
33. _M. (Stenocranius) miurus_, 51169, Lake Schrader, Brooks Range, Alaska.
34. _M. (Stenocranius) gregalis_, 8059, "Eastern Europe."
35. _M. mexicanus mexicanus_, 63094, Valle de Bravo, Estado de México, México.
36. _M. mexicanus mogollonensis_, 63298, Mt. Taylor, Valencia Co., New Mexico.
37. _M. californicus_, 76828, 1 mi. NE Berkeley, California; (_d_) ventral view.
38. _M. (Arvicola) richardsoni_, 42454, 31 mi. N Pinedale, Sublette Co., Wyoming.
39. _M. richardsoni_, 37903, 23-1/2 mi. S, 5 mi. W Lander, Wyoming; distal end.]
[Illustration: FIGURES 40-49. Bacula of microtines. Unless indicated otherwise views are (_a_) of the dorsum, (_b_) the right side, and (_c_) the proximal end with the dorsal surface upward.
40. _Microtus (Pitymys) parvulus_, UF 1508, 1 mi. W Micanopy, Florida.
41. _Microtus townsendii_, 79186, Sec. 33, T. 11S, R. 5W, Benton Co., Oregon.
42. _Microtus (Herpetomys) guatemalensis_, 65895, 2 mi. S San Juan Ixcoy, Guatemala.
43. _M. guatemalensis_, 65921, 10 mi. E, 4 mi. S Totonicapan, Guatemala, dorsal view of tip.
44. _Microtus oeconomus_, 43048, Kelsall Lake, British Columbia.
45. _Microtus (Chilotus) oregoni_, WBQ 3-C-248, 5 mi. N Orick, California.
46. _Lagurus (Lemmiscus) curtatus_, 26053, 9 mi. S Robertson, Uinta Co., Wyoming.
47. _Microtus (Chionomys) nivalis_, 65127, Wetterstein, Germany, orientation uncertain.
48. _Microtus (Chionomys) longicaudus_, 50253, Crane Flat, Mariposa Co., California.
49. _Neofiber alleni_, 27268, 2 mi. S Gainesville, Florida, orientation uncertain.]
(_Microtus_) _provectus_ (the last three are probably insular derivatives of _M. pennsylvanicus_), _M._ (_Microtus_) _fulviventer_ (perhaps derived from the same stock as _Microtus mexicanus_), _M._ (_Microtus_) _xanthognathus_ (perhaps related to _Microtus chrotorrhinus_), _M._ (_Microtus_) _coronarius_, and _M._ (_Pedomys_) _ludovicianus_.