424 PROCEEDINGS OF THE ACADEMY OF [1896. 



by many species ; short and stout forms apparently succeeding bet- 

 ter among dead leaves and the short herbage in stony places, while 

 more elongated medium-sized forms are more in vogue among those 

 which live on trees and high shrubs. It may also be the case that 

 ■when hibernating, affixed to a branch or leaf stalk, a form simulat- 

 ing a bud or spine would to a certain extent be protected from 

 thrushes and other mollusk-eating birds. 



In the matter of color, selection undoubtedly has much influence. 

 Subtranslucent browns and pinkish flesh-color harmonize with dead 

 leaves, and the opaque tracery of yellowish streaks so common on the 

 ground loving species obviously adds to the difficulty of recognizing 

 the snail in such localities. Among the lava rocks sienna browns 

 flecked with white are common and unquestionably protective. On 

 trees everywhere the tendency is to spiral stripes of color, the sur- 

 face is frequently more polished, the color brighter, with a tendency 

 to the development of green among the colors, which is, so far as I 

 know, never found in species living on the ground. In Achatinella 

 these tendencies may be studied with advantage, and they can be 

 recognized in the Ncesioti and other Bulhmdi almost everywhere. 

 They are recognizable also among the Helices. In insular faunas 

 the Helices which seem to persist most effectively are small with 

 many whorls, a wrinkled surface, yellowish or olive coloration often 

 with reddish radiating flecks when fresh, or wholly reddish-brown. 

 Many of them have a protective armature of lamellre obstructing 

 the aperture, perhaps against the hard round-bodied millipedes, like 

 Julis, which eat snails and are not uncommon in insular faunas. 



In an insular or isolated fauna, under the conditions we have 

 assumed, we should expect to find under the bulimoid forms (even 

 in a limited number of species derived from a still more restricted 

 number of ancestral types) a globose, a medium and a very attenu- 

 ated type. This is well-illustrated in almost all the faunas, as in 

 the Hawaiian Islands (Achatinellidce), Bulimuli of Lower Califor- 

 nia, Galapagos Islands and St. Helena. Leaving out the more nor- 

 mal or medium type, a few examples may be mentioned : 



Locality. Globose. Very slender. 



Hawaii, A. kauiensis, etc. A. s^ibula, plicata, etc. 



Galapagos, B. Darivinii, nux, B. Haheli, chemnitzoides. 



St. Helena, B. auris-vulpina, B. melauioides. 



Lower Cala. B. suffiatus, pilula, B. artemesia. 



