AMERICAN SPECIES OF VERTIGO. 117 



22a. Vertigo coloradensis basidens Pils. & Van. PL 12, fig. 15. 



Cylindric-oblong, with strongly striate middle whorls, and 

 with a parietal lamella only on the parietal wall, as in 

 V. coloradensis ; but having a small, short basal fold within 

 the junction of eolumellar with basal margins; the lower 

 palatal fold is especially long; there is a more or less distinct 

 callus running upward from the outer end of the upper palatal 

 fold ; finally, there is a wide and more or less prominent crest 

 behind the lip. Length 1.8, diam. 0.95 mm. 



New Mexico: Bland, Bernalillo Co., Ashnmn, type loc. 

 Colorado: Rio Blanco, Cockerell. Montana: Ward, L. E. 

 Daniels. British Columbia: Field, S. Brown. 



V. coloradensis basidens PILSBRY & VANATTA, Proc. A. N. S. 

 Phila. 1900, p. 604. 



The palatal folds, especially the lower, are decidedly longer 

 than in V. gouldi. The crest is rather broad and sometimes 

 decidedly prominent, more so than in any closely related form. 



Two specimens from Field measure : 1.75 x 1.05 and 1.95 x 

 1 mm. Those from Ward, Mont., have the crest especially 

 strong and light-colored, and the callus above the upper 

 palatal fold is quite heavy. 



22&. Vertigo coloradensis arizonensis Pils. & Van. PL 12, 



figs. 14, 16. 



Shell cylindric-oval, rimate, very small; very densely and 

 sharply but most minutely striate ; light brown. Whorls con- 

 vex, the last tapering below, the last half whorl narrow as 

 though pinched at base, flattened over the position of the 

 palatal folds, then rising in a low, hardly noticeable crest, 

 obsolete except near the base. Aperture irregularly truncate- 

 oval, the peristome well expanded, brown. Denticles 5, the 

 parietal lamella high and strong, a minute angular lamella 

 standing near its outer end. Columellar lamella entering 

 obliquely, ascending a little. Upper and lower palatal folds 

 very long, rising conically in the middle, distinctly showing 

 through from the outside, the lower fold being a little stronger 

 and more immersed, its position marked by a depression out- 

 side. There is no palatal callus. 



