184 PROCEEDINGS OF THE ACADEMY OF [March, 



stone. Living specimens were taken only on the last mound of the 

 talus at the head of the wash, shown on the left in fig. 5. This mound 

 is about 30 or 40 feet high, about 100 feet long, and has a great rock 

 in the middle. Dead shells were scattered over the talus for about 

 200 yards westward, nearly as far as the large rocks shown in the 

 edge of the pinons. Except where pifions are shown, the slope is 

 covered with shrubs. The Oreohelices live among moss and grass, 

 around and under stones in great profusion. With them live Cochli- 

 copa, Pupilla, etc., and Sonorella coloradoensis, the latter found over 

 the whole talus shown in fig. 5, but everywhere very scarce. Numerous 

 other taluses at and below the same level w T ere searched, but no other 

 colony of Oreohelix was found. All other colonies of Oreohelix seen 

 are on the upper slopes only a short distance below the rim of the 

 canyon. 



In the absence of any source on the lower levels, O. y. profundorum 

 must have been derived from O. y. extremitatis, which inhabits the 

 slope above the cross-bed sandstone, whence individuals have fallen 

 into the abyss. The considerable divergence of the race on the 

 lower level, and the fact that only one colony was found at that level, 

 seem to indicate that most snails which are carried or fall over the 

 cliff do not survive the terrific drop of several hundred feet. 



In the series of several thousand shells taken there was one sinistral 

 example. 



That the colony of O. y. profundorum is decadent seems to be indi- 

 cated by the fact that dead shells were found over an area many times 

 greater than that now inhabited by living snails. The markedly 

 senile character of the shells also foretells approaching extinction. 

 Yet the local conditions appear altogether favorable and living indi- 

 viduals are very abundant in a limited area. 



Oreohelix yavapai extremitatis n. subsp. PI. XII, figs. 15-21. 



At Station 2, near Bass's Trail, about 200 feet below the rim of the 

 Grand Canyon, the Oreohelices (pi. XII, figs. 18-21) are more depressed 

 than O. y. profundorum, less solid and less calcareous, invariably two- 

 banded. The surface is more or less suffused with light brown, espe- 

 cially on the spire, and the very thin pellucid cuticle is retained, so 

 that the shell has a slight luster. The embryonic whorls are like 

 profundorum; the first third or half of the last whorl is acutely carinate 

 in front, and the latter part descends very little (as in fig. IS, 67 per cent, 

 of the shells examined) or somewhat deeply (fig. 19, 33 per cent.). 

 Widely spaced granose spirals (such as are characteristic of O. yavapai) 



