1922] NATURAL SCIENCES OF PHILADELPHIA 87 



actually prove to be true Eremariontas, which would cause the 

 areas inhabited by the two groups slightly to overlap. So far as 

 at present known, Micrarionta s. s. is confined to the islands and 

 adjacent mainland of California and northern Lower California. 

 The typical section seems now to be restricted to the islands the 

 section Xerarionta alone occuring upon both islands and mainland. 

 An examination of these maritime forms shows that although 

 subject to much variation in form and sculpture as among them- 

 selves, so as to fall readily into several fairly well delimited sub- 

 groups, they all agree in having a nuclear sculpture of simple, 

 wavy, or anastomosing radial riblets, often obsolete, but not 

 papillose or only obscurely so, and never, so far as I ha\ e been 

 able to discover, showing a definite system of elongate papillae 

 as in the desert species. 



Eremarionta, then, is evidently wholly and characteristically 

 Lower Sonoran in a faunal sense. It is probably also, at least in 

 large degree, characteristic of what mammalogists and others have 

 denominated the Rupestrine association of that zone. 



Possibly both groups will eventually find a place as subgenera 

 of one of the other West American genera. 



Micrarionta aquae-albae new species. Plate VIII, fig. 2; Plate IX, figs, 2-6. 



Shell small, thin, depressed-conic, umbilicate, the umbilicus 

 deeply permeable, its diameter contained about six times in that 

 of the shell. Whorls four, convex, subcarinate, with deeply 

 channeled sutures, the last whorl only slightly descending in front. 

 Aperture ample, obscurely angulate at the periphery, strongly 

 oblique, its deflection about 40°. Peristome thin, sharp, not 

 reflected except slightly at the umbilicus, its edges strongly con- 

 verging and connected by a thin parietal callus. Pcriostracum 

 slightly dehiscent, rather harsh and coarse for the size of the shell, 

 being roughened not only by the lines of growth, but by a very 

 close, fine, everywhere persistent, radial wrinkling, and by an 

 overlying system of small papillae, which are elongate and so 

 crowded as to be almost anastomosing on the first whorl, subse- 

 quently becoming more distinct, granular in appearance, and 

 evidently ranked in fairly well defined, forward slanting lines. 

 Papillae on body whorl show a progressively less regular arrange- 

 ment until on the base they become smaller and more crowded 

 and their linear arrangement is no longer evident. Color of dry 

 shell near Saccardo's umber of Iiidgway, slightly lighter below, 

 with a narrow, very obscure sepia band just above the periphery. 

 Body whorl of shell on living animal snuff brown, with sepia spots 

 where mantle pigment shows through. Color of animal, — upper 

 portion of body slate, the margins neutral gray; mantle a little 



