NoHh Americcm Helicidoe. 11 



Troostiana, in whicli it is slightly emarginate near the tip, — 

 but much more so in jAicata, while the parietal tooth in Dor- 

 feuilliana is rather quadrate. The teeth on the peristome in 

 fatigiata and Troostiana are much alike, as regards form, size, 

 and position, — the superior one being the largest, — both are 

 larger and transverse in Dorfeuilliana and in plicata. the 

 inferior one being the largest in the latter. Behind the peri- 

 stome there are two small pits, showing the situation of the 

 teeth in fatigiata and Troostiana, while there is scarcely more 

 than a deep, well marked constriction in Dorfeuilliana. H. 

 Troostiana has a slight groove on the inner side of the last 

 whorl, the absence of which in fatigiata is noticed by Say, 

 but I scarcely consider that a good specific character. Fresh 

 specimens of H. fatigiata are, I believe, covered with a very 

 thin epidermis, on which hairs are sparingly scattered, — the 

 scars of the hairs may be detected, especially on the last whorl, 

 in denuded shells. 



H. fatigiata has, at a short distance within the aperture on 

 the base of the last whorl, a small, detached, erect, rounded 

 tubercle, answering probably the same j)urpose in the economy 

 of the animal, as the "fulcrum"* originally noticed by Mr. Lea 

 (Observations Vol. Y. p. 80) in H. spinosa, though of a 

 different construction. 



The measurements of my specimens agree with those given 

 by Shuttleworth. 



For further illustration of the differences in the species in 

 question, I refer to the accompanying figures. 



* In his "Notes on American Land Shells" (Proc. Acad. Nat. Sc, Phila. Oct. 

 1857), Mr. W. G. Binney mentions having a specimen of H. fallax Say, in which 

 there is "a well developed fulcrum as in H. spinosa, &c." I should explain that 

 he received the specimen referred to from me (one of several given to me by 

 Dr. Budd), and that it is by no means H. fallax, — rather a very large fonn of If. 

 vultuosa Gould, or its close ally. In the latter species, as well as in Mr. Binney's 

 shell, there is a short, somewhat transversely elongated tubercle, not i-ounded 

 and obtuse, though in the same situation as in ff. fatigiata. There is no such 

 process in H. fallax. 



