244 Mr. W. H. Benson on Plectopylis. 



ing no true plicate barriers, and furnished with only a few 

 lamellae running longitudinally to a moderate distance within 

 the aperture. Pfeiffer refers the whole of these shells to Ophio- 

 gyra; and Messrs. H. and A. Adams include them all in Gorilla, as 

 a section of Anchistoma. Again, Helix pledostuma, B., is referred 

 by Albers to Gonostoma, synonymous with Polygyra, Say and 

 Pfeiffer, and with Polygyra as a section of Anchistoma, H. & A. 

 Adams. These include Helix obvoluta, H. angigyra, H. Corcy- 

 rensis, and other shells which exhibit no traces of pylaic plica- 

 tion. It therefore becomes necessary to separate the first divi- 

 sion from H. Rivolii and its congeners, and the second from 

 H obvoluta and its allies. Together they will form a natural 

 group divisible into three sections conformably with the varying 

 structure of the plicate pylse ; and as the type of the first group 

 was announced in a former paper as being ovoviviparous, there 

 may exist grounds for generic separation from Helix equally 

 strong with those which authorize the distinction of Par-tula 

 from Bulimus. I name the group 



Plectopylis. 



Testa plerumque sinistrorsa, late umbilicata, subdiscoidea, depressa 

 vel conoideo-depressa ; apertura plica parietal! callosa lamellam 

 horizontalem saepe emittente, intus pylis sive epiphragmatibus 

 pluribus distantibus plicatis (prima ab apertura plus minusve 

 remota) obstructa. 



The typical section comprises species in which the pylaic 

 epiphragms consist of a strong vertical parietal lamina, with a 

 tortuous support on the inner side, and giving out towards the 

 aperture various horizontal lamellse, another independent hori- 

 zontal plica crossing near its base ; while the palatal portion 

 -consists of three horizontal plicae above, one below, and a large 

 transverse vertical lamina which corresponds with and crosses 

 behind the outer portion of the dichotomous parietal lamina. 

 It comprehends 



Helix Achatina, Gray. 



Cyclaspis, B. 



The second section consists of species in which the parietal 

 vertical lamina is more simple than in the first, being scarcely 

 dichotomous, but provided with anterior lamellae; while there 

 are six long or short, straight or sinuous, horizontal palatal 

 plica?, the fifth of which in one species has a tendency to simu- 

 late the vertical lamina of the previous section, and some double 

 ])lica) in the other point towards the 3rd section. It comprehends 



Helix refuga, Gould, var. dcxtrorsa. 



Leiophis, B., n. s. 



