1899.] NATURAL SCIENCES OF PHILADELPHIA, 193 



A. miorhyssa (Ball). 

 Polygyra miorJiyssa Dall, Nautilus, Vol. xii, p. 75 (Nov., 1898). 

 Eagle Creek, Sierra Blanca, N. M. {Ashmun and Townsend). 

 The species are unequally related. Their relationships inter se are 

 shown by the following keys for the determination of known forms:' 



a. — Aperture strongly trideutate Thomsonmna. 



a'. — Aperture toothless or without teeth on the outer lip. 

 b. — Diameter less than double the altitude. 



rhyssa, including miorhyssa. 

 b'. — Diameter about double the altitude. 



c. — Surface heavily ribbed; a slight basal tooth or none. 



altissima. 

 c'. — Surface nearly smooth. , 



d. — Basal lip with two contiguous teeth; a parietal 



tooth or none pseiidodonta. 



d'. — Basal lip toothless. 



€. — Whorls 5; diam. 12-14 mm. . Ashnuni. 

 e'. — Whorls 6; diam. 16-19 mm.; pei'istome 



slighter chiricakuana. 



The three main groups indicated in the above table are Thom- 

 soniana — rhyssa including miorhyssa and hyporhyssa — altissima, 

 pseudodonta, Ashmuni, chiricahuana. 



Mr. Cockerell arranges the forms somewhat differently, thus : 



1. Aperture hardly dentate, with at most a small parietal denticle 



and a callus or pair of low and small denticles on the basal 



part of the aperture 2 



Aperture strongly dentate, both on the parietal wall and lip; 

 whorls 5^ Thomsoniana (Ancey). 



2. Shell distinctly ribbed 3 



Shell striate or nearly smooth 4 



3. Compact, spire elevated; diam. 15-17 mm. . /-/ipsa (Dall). 

 Small and flat; diam. 12 mm alils8im,a (QkW.). 



4. Shell compact, with rounded whorls; spire elevated ; last whorl 



large ; striation well marked 5 



Flattened, with a depressed spire ; shell feebly striate or nearly 

 smooth, with more or less distinct spiral incised lines ; umbili- 

 cus wide, broadly exposing»the penultimate whorl. . . 6 



^ The first key is by Mr. Pilsbry, the second by Mr. Cockerell. 

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