74 



KORTH AMEEICAN" FAUNA. 



[No. 38. 



young adult collected at Lake City, Modoc County, Cal.; in the 

 original description Merriam mentions the following cranial and 

 dental characters: 



^kull similar to that of S. calif amicus, but slightly smaller, with narrower palate 

 and decidedly narrower and more slender rostrum. Last upper premolar with a 

 strongly developed, trenchant inner cusp, not present in californicus} 



The narrowness of the palate and rostrum is probably due in 

 part to immaturity; the skuU of a young adult female, which has 

 been removed from an alcohohc specimen ^ from Fort Klamath, 

 has the rostrum as narrow as that of the type of truei though it is 

 sUghtly shorter. The presence of an inner cusp on the last upper 

 premolar is not of diagnostic value. In any large series of Scapanus 

 from a single locahty this cusphke process may be present in various 

 stages of development in about half the specimens; it appears more 

 frequently in skuUs of young individuals and seems to be absorbed 

 with age. In the type of truei this accessory cusp has about reached 

 its maximum development, yet in a specimen ^ collected as nearby 

 as Cedarville, Modoc County, there is a barely perceptible trace of 

 a cusp. 



Considerable local geographic variations are observed in this 

 form, but to recognize them by subspecific names would only be con- 

 fusing. With a large series of specimens available from each of many 

 locahties it would be possible to learn more of the extent and rela- 

 tionships of these variations. Specimens from the upper Sacra- 

 mento Valley show intergradation with S. I, latimanus, the color 

 darkening and the skulls becoming larger and more elongate. A 

 specimen from Fremont, Oreg., has certain cranial characters 

 which suggest tjiat dilatus may possibly intergrade with S. o. 

 schefferi in central Oregon. 



Specimens examined. — Total number, 44, as follows: 



California: Auburn, 1;^ Baird, 1; Bald Mountain, 1; Cedarville, 1;^ Chico, 1; 



Fort Crook, 1; Hayden Hill, 1; Lake City, 1; McCloud, 2; McCloud River, 

 ^ 1;^ Millford, 2; Mosquito, El Dorado County, 1;^ Mount Shasta, 1; Nevada 



City, 1; Parker Creek, Warner Mountains, 1;^ Plumas County, 1;^ Pratt- 



ville, 1; Quincy, 4; Red Point, 1;* Round Mountain, Shasta County, 1; 



Sisson, 6;^ Susanville, 4;* Tower House, Shasta County, 1.^ 

 Nevada: Holbrook, 1. 



Oregon: Ashland, 3; Fort Klamath (type locality), 3; Fremont, 1. 



1 Merriam, C. H., Proc. Biol. Soc. Washington, vol. 11, p. 102, 1897. 



2 No. 186627, U. S. Nat. Mus., MeiTiam collection. 



3 No. 16723, Mus. Vert. Zool., Univ. California. 

 * Collection Stanford Univ. 



s Collection Mus. Vert. Zool., Univ. California. • 



6 Collection Amer. Mus. Nat. Hist. 



7 Collection Carnegie Mus. 



