1913.] NATURAL SCIENCES OF PHILADELPHIA. 389 



have varying forms, which for the present I have designated by 

 numbers, as follows: 



(1) Asuncion Island, not far below Turtle Bay, has a somewhat 

 differing race (pi. XVI, fig. 48). The bands, translucent instead of 

 brown, are usually fewer and broader — five or six, or sometimes as 

 many as ten. Granulation indistinct or obsolete. Diam. 16 to 

 19 mm. All the specimens seen from this tiny, barren islet were 

 dug out of fine sand. It probably occurs only fossil. It is much 

 like Pfeiffer's figures of levis, but the granulation is scarcely visible^ 



(2) Var. crassula Dall (pi. XV, fig. 24) from Natividad Island 

 (south of Cerros) is like the preceding in having few translucent 

 bands, about 6 in the cotype figured. It is somewhat heavier than 

 levis of equal size, and is a little more elevated. No granulation is 

 now visible on the corroded surface. The columellar callus is heavy 

 and prominent. Alt. 15, diam. 17 mm., with nearly oh whorls 

 {levis of the same diameter has f of a whorl less). Fossil. 



(3) The variety from San Geronimo Island (pi. XVI, figs. 49, 50,. 

 coll. by H. N. Lowe) resembles crassula in contour and banding. 

 It is not quite so heavy, has a half whorl less, and is well enough 

 preserved to show traces of granulation on the spire in some examples. 

 It was found fossil. Specimens measure: 



Alt. 



It appears that on these small, barren islets the levis stock has 

 deteriorated in size, often becoming more globose, and finally has died 

 out. The weak sculpture and usually small number of bands (in 

 comparison with Turtle Bay levis) are probably ancestral characters^ 

 preserved in these isolated colonies. So far as I know, these dimin- 

 ished races are extinct. The bands of these helices, brown or blackisk 

 in life, become translucent gray in long dead or fossil specimens. 



(4) M. levis globosa n. subsp. PL XVI, figs. 46, 47. The shell 

 is glohose-conic, higher than levis, with very little of the granulation 

 of that species, solid, glossy, multilineate with brown on a white 

 ground, or sometimes bluish-white without bands. Columella strongly- 

 toothed. Alt. 20.3, diam. 22.3 mm., 5^ whorls; or higher, alt. and 

 diam. 22 mm. Cerros Island, living. Probably Binney's two out- 

 side figures 311, in Land and Fresh-water Shells, I, p. 177, represent 

 this race. 



