groenlandicus, 52524, Point Barrow, Alaska.

Figures 14-25. Bacula of Microtus. Unless indicated otherwise views are (a) of the dorsum, (b) the right side, and (c) the proximal end with dorsal surface upward.

1. M. pennsylvanicus, 42439, 1 mi. S, 2 mi. E Eagle Nest, Colfax Co., New Mexico; abnormality perhaps owing to injury; dorsal view.
2. M. pennsylvanicus, 42306, 5 mi. N, 26 mi. W Saguache, Colorado; dorsal view.
3. M. pennsylvanicus, 43043, 20 mi. NE Anchorage, Alaska, ventral view.
4. M. pennsylvanicus, 42430, 1 mi. S, 2 mi. E Eagle Nest, New Mexico.
5. M. agrestis, 67102, Gryon, Switzerland.
6. M. montanus amosus, 62241, 1/2 mi. E Soldier Summit, Wasatch Co., Utah.
7. M. montanus nanus, 57470, 2 mi. N, 2 mi. W Pocatello, Idaho.
8. M. montanus fusus, 42307, 5 mi. N, 26 mi. W Saguache, Colorado.
9. M. arvalis, 67101, Vidy, Switzerland, possibly not mature.
10. M. guentheri, 67104, Palestine.
11. M. orcadensis, 67106, Orkney Islands, orientation uncertain.
12. M. fortis, 63841, Chipo-ri, Korea, (d) ventral view.

Figures 26-39. 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.

1. M. (Pitymys) fatioi, 67103, Zermatt, Switzerland, immature.
2. M. (Pitymys) pinetorum, 76834, 2 mi. N Baldwin, Douglas Co., Kansas.
3. M. (Pitymys) pinetorum, 68545, 1 mi. NE Pleasant Grove, Kansas.
4. M. (Pitymys) quasiator, 30709, Teocelo, Veracruz, (d) ventral view.
5. M. (Pitymys) quasiator, 19878, 5 km. N Jalapa, Veracruz.
6. M. (Pedomys) ochrogaster, 75036, 1 mi. N, 2 mi. E Oberlin, Kansas.
7. M. (Stenocranius) miurus, 51152, Lake Schrader, Brooks Range, Alaska.
8. M. (Stenocranius) miurus, 51169, Lake Schrader, Brooks Range, Alaska.
9. M. (Stenocranius) gregalis, 8059, "Eastern Europe."
10. M. mexicanus mexicanus, 63094, Valle de Bravo, Estado de México, México.
11. M. mexicanus mogollonensis, 63298, Mt. Taylor, Valencia Co., New Mexico.
12. M. californicus, 76828, 1 mi. NE Berkeley, California; (d) ventral view.
13. M. (Arvicola) richardsoni, 42454, 31 mi. N Pinedale, Sublette Co., Wyoming.
14. M. richardsoni, 37903, 23-1/2 mi. S, 5 mi. W Lander, Wyoming; distal end.

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.

1. Microtus (Pitymys) parvulus, UF 1508, 1 mi. W Micanopy, Florida.
2. Microtus townsendii, 79186, Sec. 33, T. 11S, R. 5W, Benton Co., Oregon.
3. Microtus (Herpetomys) guatemalensis, 65895, 2 mi. S San Juan Ixcoy, Guatemala.
4. M. guatemalensis, 65921, 10 mi. E, 4 mi. S Totonicapan, Guatemala, dorsal view of tip.
5. Microtus oeconomus, 43048, Kelsall Lake, British Columbia.
6. Microtus (Chilotus) oregoni, WBQ 3-C-248, 5 mi. N Orick, California.
7. Lagurus (Lemmiscus) curtatus, 26053, 9 mi. S Robertson, Uinta Co., Wyoming.
8. Microtus (Chionomys) nivalis, 65127, Wetterstein, Germany, orientation uncertain.
9. Microtus (Chionomys) longicaudus, 50253, Crane Flat, Mariposa Co., California.
10. 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.