226 AMERICAN JOURNAL 



sparingly on the west slope down to about 3650 ft. in lat. 39°, 

 (Rowell), and at the other points before mentioned. No speci- 

 mens of Helicoids have been found on the mountains south of 

 the lake, where they rise to the height of 15000 ft., the general 

 granitic formation, and perpetual snow above 8000 ft., prevent- 

 ing their growth. It appears, however, that these minute species 

 as well as fresh-water mollusca can exist where there is but an 

 infinitesimal quantity of lime in the soil.* 



At the " Big Trees " of Calaveras Co., 4750 ft. above the 

 sea, Master W. Hillebrand discovered the interesting Conulus ? 

 chersinella, Dall, (perhaps rather a Uyalina) the only locality 

 yet discovered for it. 



No large Helicoids have been found above 4000 ft. elevation 

 in these mountains, though extending higher in the coast range 

 and even in the Rocky Mountains in lat. 47°. 



The reason seems to be as follows : The large Helicoids 

 evidently require a considerable amount of lime in the soil, or 

 rather in the vegetation on which they feed, and that requires it 

 in the soil. Thus none of them are found in the Sierra Nevada 

 above the belts of limestone which cross out on its western slope, 

 though in many places the climate and other conditions seem 

 favorable to them. In fact they are scarce below that level 

 except on or near the limestone belts, and abound only in very 

 limited tracts where it is the prevailing rock. Beginning at 

 Fort Tejon, lat. 35°, the limit of H. Traskii in this direction, we 

 find, by Prof. Whitney's report, that there is a ridge of limestone 

 running northwest into the coast range at that place, and there 

 are besides abundant cretaceous fossils where the Helix is most 

 numerous. The lime here reaches an elevation of about 4000 

 feet. At Fremont Pass, which is at the southern end of the 

 Sierra, a similar limestone ridge begins, and extends northward 

 along the western slope, being at an elevation of 4000 ft. in the 

 pass and apparently becoming somewhat lower in going north- 

 ward. Mr. King crossed it twenty miles east of where the 

 Kaweah emerges from the mountains, or 35 east of Visalia, 

 and all the streams south of there contain boulders of it. Yet 

 at Visalia, where there is a splendid and extensive oak forest, 

 growing on a granitic alluvium, I could find no trace of Helicoids, 

 though H. tudiculata was common at the point where White 

 River emerges, probably not over ten miles west of the limestone 

 vein. It has not been traced through Fresno County, but prob- 



* The vast range of some of these minute species is explicable by the 

 fact that their still smaller eggs, or even the shells themselves, are very 

 likely to adhere to the feet of migratory birds, and to live, when washed 

 off in a favorable place, like the equally wide spread Limneidse. 





