PUPOIDES. 117 



This toothless cylindric snail resembles the following 

 species, but is quite unlike any other of our fauna. It was 

 one of our rarest and least known species before 1900, but 

 since that time has often been taken in abundance. Its earlier 

 adventures under various aliases have been discussed in my 

 paper of 1900. 



Gabb did not notice the ribs, which are often partially lost 

 by wear, but they are present though weak by wear in the 

 only one of his specimens preserved. The original description 

 follows. 



Pupa hordacea Gabb. Description. Shell very small, cylin- 

 drical ; apex obtuse ; whorls 6, convex ; suture well impressed, 

 smooth, thin, horn-color; aperture small, rounded below, un- 

 armed, lip narrowly reflected and white; base umbilicate, the 

 umbilicus bounded by an angle. 



Dimensions. Length .11, width .04 inch. 



Locality. With the preceding [Fort Grant, near the junc- 

 tion of the Arivapa and San Pedro rivers, Ariz. Collected by 

 Dr. G. H. Horn]. 



This is a species of the arid plateaus and foothills, never 

 found in the humid upper zone of the mountains. It is 

 known by specimens taken in the debris of streams or in 

 Pleistocene or later deposits. The Mesilla specimens may 

 have floated from the upper river ; those from the San Pedro 

 at Benson certainly ame from further south, and the type 

 lot also may have been from the San Pedro drift. Westward 

 from Benson, in Pima County, we saw nothing of it; but it 

 penetrates westward further north. It appears to be most 

 abundant in the northern counties of Arizona, extending 

 north to San Miguel Co., Colorado, near the Utah line. 

 Specimens from this place measure from length 4.15, diam. 

 1.6, aperture 1.4 mm., barely 6 whorls, to length 3.3, diam. 

 1.6, aperture 1.3 mm., 5*4 whorls. 



In the deposits at Las Vegas, N. M., at its northeastern ex- 

 treme limit, it occurs with P. inornatus, which here reaches 

 its southern limit as now known. The localities follow. 



Colorado : Dolores canyon at mouth of Gypsum Creek, San 

 Miguel Co. (Junius Henderson, 1914). 



