North American Helicidce. 289 



racters. 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 some- 

 what differently placed. In the striae it differs much, these being 

 larger, much better defined, and passing over the whorls. In the umbi- 

 licus 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 exceed- 

 ingly alike, viz. P. fatigiata Say, P. plicata Say,* and P. Dorfeuilliana 

 Nob." 



As already mentioned, Binney gives a figure of this species 

 in the Boston Jl. as fatigiata Say, and in the Terr. Moll, as 

 plicata Say. 



In Pfeiffer's Mon., in Chemnitz (ed. 2), and in Reeve's 

 Conch. Icon, no doubt is expressed as to Troostiana being a 

 good species. The figures in the two latter works appear cer- 

 tainly to be of Lea's shell. 



Deshayes, in Fer. Hist., refers to its close affinity with his 

 Dorfeuilliana {fatigiata Say), of which he is inclined to treat 

 it as a variety, — the figure to which he refers (PI. 69 D. fig. 4) 

 is not altogether satisfactory. 



Shuttleworth in Diag. n. Moll. (1852), as already quoted, 

 erroneously considered Troostiana Lea identical with plicata 

 Say, and in his observations on H. Dysoni,\ in the same work, 

 as scarcely more than a variety of Dorfeuilliana Lea, but he 

 subsequently entertained a different opinion, as I shall pre- 

 sently explain. 



Lea's description is unfortunately meagre, and his magnified 

 figure, copied on PL IX. fig. 22, does not correctly show the 

 parietal tooth, — its form, indeed, as figured, might be referred 

 to H. plicata, but the size, form, and position of the two 

 other teeth agree with Troostiana. 



* Mr. Lea in his remarks on //. Troostiana and H. Dorfeuilliana, refers to H. 

 plicata Say, but in fact alluded to H. pustula Fer., labelled plicata Say in his 

 cabinet. 



f For copy of the description and observations on this species see p. 295. 



