300 JMiOClCKDINCiS OF THE ACADEMY OE [1890. 



tluir a native Aiuerican one, lead nie to associate them under the 

 oldest name, Polygijra, in my check-list of our land shells.^ 



So much for tlie one side. And on this side there is full as much 

 danger in holding extreme views, as on the side of excessive analysis. 

 Let us not profess sweeping views on coalescence of minor groups 

 until we have the species which actually show transition ; and (to 

 pass from generalizations to a special case), it may be noted here 

 that while the species of the Polygyra-\- Triodopsis-{-Mesodon-\-Steno- 

 trema group, invariably have a reflected lip, tlie two species belong- 

 ing (as I claim) to Folygyrella have a blunt lip, not in the least ex- 

 panded or reflexed. I prefer to keep very different things apart. 



Dr. Cooper's original description is excellent, but the figures are 

 bad. The latter are copied by Tryon in the Manual of Conchology, 

 Binney describes a wholly different shell in his two publications — 

 a shell which has, he states, an expanded lip. In his Manual of 

 American Land Shells the species is said by him to have four whorls 

 and is placed in Polygyra. Still later (3rd Supplement to Terr. 

 Moll. V.) Mr. Binney seems to entertain a suspicion that the Trio- 

 dopsis Roperi Pils. (which he strangely enough places in Polygyra !) 

 is the same species. The mistakes and inconsistencies of this record 

 would be indeeel perplexing were it not for the fact that Mr. Binney 

 has never seen the H. Harfordiana. A single examination would 

 doubtless have convinced him that it is, as Dr. Cooper states in his 

 original description, most intimately allied to Polygyrella jjolygyrella. 

 Figure 81 of the Manual of American Land Shells is incorrect in 

 showing the parietal tooth too far within the aperture. The original 

 figures have the same defect. 



With Polygyrella polygyrella this species agrees in general form, 

 color, sculpture and texture, as well as in the form of the aperture 

 and the blunt, not at all expanded lip. In texture and character of 

 the lip both species are very different from Polygyra and Triodopsis ; 

 the species of these last two sections have the lip expanded and re- 

 flexed. 



The section Polygyrella may be defined thus: 



Shell disk-sliaped, the spix'e nearly flat, periphery rounded, even 

 in the young ; umbilicus vvide within, showing all the whorls. 

 Texture somewhat vitreous and subtranslucent ; ribbed-striate above, 

 polished beneath ; color yellow, yellowish-green or light brown. 

 Whorls six to eight, narrow, slowly widening, the last a trifle descend- 



1 Proc. Acad. N. S. Phila. 1889, p. 193. 



