248 CALIFORNIA ACADEMY OF SCIENCES. 



among the damp leaves of dark forests, and then carry them 

 to new localities perhaps very far distant. I thus account 

 for the new appearance of species in spots that have been 

 before searched for years. Thus after eight years residence 

 at Hay wards, California, I found in 1883, one lone specimen 

 (living) of Hyalina arborea, never before found in the 

 county, just as I found a few dead specimens of this species 

 (var. Breweri) in San Francisco County, in 1869, its only 

 occurrence there. 



I have also found dead specimens of H. minuscula near 

 Haywards, in a spot where the native trees had been closely 

 cut and burned off, but nowhere else, though it has been 

 found in other parts of California. It may again appear 

 suddenly, like arborea, in a favorable place. Indeed, as is 

 well known, these Helicellidce are much less limited in range 

 than large forms, being easier diffused by birds, and requir- 

 ing less shelter and lime. In 1862 I found one H. limutala 

 near San Mateo. It is, therefore, not safe to assume that a 

 small species is extinct until much more search is made. It. 

 may reappear where least expected, like the Helicina, so 

 long believed extinct in the East, and may spread very rap- 

 idly by the aid of birds, in spite of its " snail's pace." 



4. SUB-FOSSIL SPECIES. 



The extinction of the large land animals, probably by 

 cold, was as complete in the coast ranges as in the Sierras, 

 and the glacial influence may also have affected the mol- 

 lusca. 



There are, indeed, a few species which have so far been 

 found only dead and bleached, all of which are peculiar 

 from being of the discoid form that may be considered the 

 simplest style of "Helix" (literally meaning a coil). One I 

 found on an island off the California coast, and is possibly 

 living in Mexico, but is undescribed. The second was 

 "found by Mr. H. Moores in the foothills of the west slope 

 of the Nevada Mts., about 5 miles south of Coloma, and \ 



