156 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Many portions of these breaks in the topography are suffi- 

 ciently marked to suggest their actual service as physical bar- 

 riers to the dispersal of animals having the sedentary habits of 

 gophers. Especially is this the case between Strawberry and 

 Tahquitz valleys, where lies the dividing line between nigri- 

 cans and jacinteus. It will be noted that Tahquitz and Round 

 valleys, as well as the country lying directly between, the en- 

 tire habitat of jacinteus in fact, is on the eastern slope of San 

 Jacinto Peak, with all drainage toward the desert. Strawberry 

 Valley, together with the rest of the habitat of nigricans in 

 these mountains, is west of the divide. There are no streams 

 connecting the higher valleys with Strawberry Valley and the 

 slopes to the westward, streams which with their narrow mar- 

 gins of favorable surroundings would offer means of dispersal 

 for these animals. Also the slopes intervening are so steep 

 and rocky as apparently to preclude the possibility of uninter- 

 rupted distribution without some such passage ways (see Univ. 

 Calif. Publ. Zool., Vol. 10, plate 8, fig. 1). 



This latter condition also prevails on the eastern side of the 

 mountain, where the series of tremendous, rocky precipices 

 descending abruptly to the desert forms an effective barrier, in 

 all probability extending from the habitat of the boreal jacin- 

 teus to that of the Lower Sonoran perpallidus of the floor of 

 the desert below. So altogether it seems probable that Thom- 

 oniys jacinteus is absolutely separated from those forms geo- 

 graphically nearest to it by the physical conditions surround- 

 ing its habitat. 



Between Tahquitz and Round valleys there is no abrupt 

 break. Although at the eastern edge of Round Valley there 

 is nearly as steep and rocky a cliff as between Tahquitz and 

 Strawberry valleys, the approach from Tahquitz Valley to 

 Hidden Lake, and thence to Round Valley, is gradual, and 

 gopher sign was seen continuously over the whole distance. 

 In accounting for the occurrence of nigricans in Strawberry 

 Valley, in common with the lower Thomas Valley and the 

 country to the southward, there is no difficulty, for while 

 Strawberry Valley occupies a sharply defined terrace, with 

 steep slopes below, the connecting streams with their adjacent 

 congenial margins are probably sufficient to explain the gen- 

 eral dispersal of this species of gopher. 



