HELIX. 89 



T. superne subplanata, inferne subinflata, cornea, longitudinaliter 

 striata, late umbilicata; anfr. 6 ; apertura lunata, tridentata. 



Sliell above neai'ly flat, below somewhat inflated, horn color ; 

 longitudinally striate, widely umbilicate ; whorls 6 ; aperture lunate, 

 three-toothed. 



Habitat. Tennessee. Prof. Troost. 



Diam. A, length .2 of an inch. 



Remarks. This species strongly resembles P. Dorfeuilliana, here- 

 in described, being nearly of the same size, and possessing most of 

 its characters. It differs, however, in the large solid tooth on the 

 left lip being more angular, and in the two teeth on the right lip 

 being somewhat differently placed. In the sti'ife it differs much, 

 these being larger, much better defined, and passing over the whorls. 

 In the umbilicus it is wider, and shows more of the two whorls. 

 This shell forms the fourth of a group, the form of the apertures 

 of which is exceedingly alike, viz. P. fatigiata Say, P. plicata 

 Say, and P. Dorfeuilliana Nob. 



As appears in the synonymy, this species has been much 

 more fortunate than its allies, having been correctly deter- 

 mined by most writers. Shuttleworth, however, errone- 

 ously refers it to plicata. 



Bland thus remarks on it : — 



Mr. Lea has kindly allowed me to examine his original speci- 

 men, which differs from mine only in having the parietal tooth 

 somewhat more emarginate. 



H. Troostiana is very closely allied to H. fatigiata Say, from 

 which I separate it with some hesitation. In its fresh state it has 

 a thin, sparingly hirsute epidermis. I have moreover two speci- 

 mens in my cabinet, (both hirsute,) which are as acutely carinated 

 a^ fatigiata, with the strige as prominent below as above, — (in one 

 more numerous,) but both having the parietal tooth of Troostiana. 



I am not altogether satisfied with the validity of Shuttleworth's 

 remark, that the superior tooth in fatigiata is larger and more 

 conspicuous than in Troostiana. 



This species has the same tubercle within the last whorl as H. 

 fatigiata. 



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