PUPILLA, AMERICAN. 169 



smaller P. sonorana, which occupies an area to the east and 

 south of syngenes, the northern colonies of sonorana being 

 separated from the nearest syngenes by the Rio Grande 

 valley. 



The type specimen has no palatal tubercle, but in most 

 colonies the lower-palatal is usually developed. There is great 

 variation in length. A lot from Spectacle Cove, Bass trail, in 

 the Grand Canyon, contains shells from 3 mm. long, of 7 

 whorls, to those 3.7 mm. of 8 whorls. Some of those from 

 the Kaibab Plateau are very long, over 4 mm., of fully 9 

 whorls. 



Mut. nivea. At Marsh Pass, Black Mesa, Navajo Co., Ari- 

 zona, Ferriss found beautiful albino specimens (pi. 18, fig. 11) 

 together with the brown ones. This mutation also occurs in 

 some Grand Canyon lots. 



"Pupilla, syngenes Pils. and P. syngenes dextroversa seek 

 the well-drained hillsides where grass roots and spawls of 

 stone lying upon the soil furnish shelter. So far they have 

 not been gathered in deep forest conditions where pupas 

 mostly congregate" (Ferriss). Both are arid country forms 

 of the plateau of northern Arizona, apparently distributed 

 generally, but not found far north of the Colorado river. 

 The records from Montana and northern Colorado, far from 

 the main herd, appear to indicate extension north in western 

 Colorado or eastern Utah, regions as yet but little explored 

 for shells. 



The record of a half specimen from Benson, Arizona (Proc. 

 A. N. S. Phila., 1915, p. 390), I now think was based on a 

 sinistral specimen of some other species. The shape of the 

 summit is not quite right for syngenes, and the later whorls 

 are wanting. That locality lies several hundred miles from 

 the nearest known locality for P. syngenes. 



P. syngenes dextroversa (P. & V.). Figs. 2, 3. 



Similar to the typical form, but dextral. The shell is sub- 

 cyliudric, a little wider near the upper end. The last whorl 

 is flattened laterally, with a strong, rounded crest followed by 

 a deep constriction behind the lip, which is thin and very 



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