1918.] NATURAL SCIENCES OF PHILADELPHIA. 285 



and robust Sonorella was found at a low elevation in a barrier of 

 boulders, so dry and barren the snails would necessarily lie dormant 

 a large part of the year. At a thousand feet higher, beside a stream 

 of running water, came in a much smaller breed; and, 1500 feet 

 above number two, with an ideal situation as to a moist atmosphere, 

 food, shelter and snail comfort, lived a pigmy Sonorella of about 12 

 millimeters in diameter. 



Again on the Kaibab Plateau in 1909, every colony of Oreohelix 

 Mrigosa depressa seemed a little different from all other colonies. 

 At Two Spring Can^yon with running water all the way, the pigmies 

 were at the higher station in a grove of quaking asp. Every colony 

 increased in size and color brilliance at a regular pace down the 

 canj^on. Here seemed proof positive of the advantage of a longer 

 growing season. Over the ridge in Snake Gulch the order was re- 

 versed, for the larger shells were at the top in a dry situation, and 

 their size seemingly decreased in proportion to the mileage as we 

 descended along a running stream. In Jacobs Canyon, running 

 parallel to Snake Gulch, dry all the way, the large and gaudy shells 

 Avere midway, the smaller and paler above and below. Food condi- 

 tions may have had some influence in the development of these 

 races but if so the evidence was not apparent. In the field we meet 

 contradictions continually beyond our understanding, but perhaps 

 we may have a better comprehension before the survey of the South- 

 west is completed. 



HELIOID^. 



Sonorella odorata n. sp. PI. Ill, figs. 1 to 4. 



The shell is depressed, umbihcate, the umbilicus contained about 

 7| times in the diameter of shell; buffy-citrine below, somewhat 

 lighter than Isabella color above, with a chestnut brown band at the 

 shoulder. The first half whorl has irregular radial wrinkles soon 

 passing into a low granulation, the last embryonic whorl granular, 

 over which there are close decurrent threads, interrupted into short 

 dashes on the upper part of the whorl. Subsequent whorls are 

 very minutely granular, somewhat dull, the granulation effaced at 

 the base, which is more glossy. The last whorl shows also numerous 

 faint spiral striae. The whorls are quite convex, the early ones 

 increasing slowly, the last widening rapidly, rather abruptly descend- 

 ing close to the aperture. The aperture is elliptical-lunate; peristome 

 is narrowly expanded throughout, dilated at the columellar insertion. 



Alt. 11.4, diam. 19.5 mm.; 4^ whorls (type). 

 " 13.4, '' 23.3 " 4f " (Station 18, 1917). 

 " 13.2, " 22 " (Station 18, 1917). 



