GUDB : ON THE AEMATURE OF LAND MOLLUSCA. 59 



Genus Polygyrella, Binney. 

 Only three species are known, all American. P. polygyrella, 

 Bid., has the mouth of the shell obstructed only by a raised, transverse 

 lamella on the parietal callus, giving off a short horizontal fold. On 

 the base, one-half of a whorl from the aperture, there may be seen 

 through the shell- wall three short, horizontal, white lamellae and one- 

 quarter of a whorl further back the remains of a former set, partly 

 absorbed. 



Genus Polygyratia, Gray. 



This genus is split up into four sections ; the first, Polygyratia, 

 S.S., with two species, one found in Brazil, the other in Bolivia. 

 The first, P. polygyratia, Born, is a large, disc-shaped shell, a 

 specimen in my collection measuring as much as 47 mm. in diameter. 

 It is provided internally with short, horizontal and oblique folds, 

 which can only be observed by breaking away parts of the shell-wall, 

 which is very thick and solid. In the specimen examined 

 three short, horizontal lamellae occur on the outer wall, one-third of 

 a whorl behind the mouth ; one-third of a whorl further back is 

 found a similar group, and in addition, facing the latter, an oblique, 

 sinuous, raised fold on the parietal wall, with a short, low, 

 horizontal lamella immediately below. The first to draw attention 

 to these structures was Moricand,^ who states that having examined 

 several specimens he found these lamellae to vary in number from 

 one to three on either side, three series usually occurring in the last 

 whorl. 



Of the subgenus Ridleya, Ancey, only one species is known, 

 P. quinquelirata, Smith, from the island of Fernando Noronha, a 

 small shell, measuring only 5 mm. in diameter. It has a small 

 aperture, which is provided with two entering, horizontal folds on 

 the parietal wall, reaching near to the aperture, two on the basal, 

 and one on the outer wall not reaching as far as the parietal, the 

 lower of the latter intercalating between the outer and basal folds. 



The section Systrophia, Pfr., contains some twenty-two species, 

 all South American, and all many-whorled forms. P. ortoni, Crosse, 

 from Ecuador, is simply deeply scrobiculate at the upper part of the 

 peristome, the corresponding tubercle causing the aperture to assume 

 a triangular shape. In P. entodonta, Pfr., however, are found three 

 short, horizontal lamellae on the outer and basal walls, some distance 

 behind the peristome. 



Genus Moellendorffia, Ancey. 



This was at first classed as a subgenus under Helicodonta by 



Dr. Pilsbry, but subsequently he modified his views as to its afl&nities 



and considered it to be closely related to Chloritis. On conchological 



as well as geographical grounds this appears to me a more reasonable 



1 Mem. Soc. Phys. Hist. Nat. Geneve, vol. xi, 1S46, p. 151, pi. v, figs. 1-3. 

 VOL. XIV. — SEPTEMBEB, 1920. 5 



