PLECTOPYLIS. 



101 



descending short ridge, while below it deflects obliquely and gives 

 off on the anterior side a comparatively short horizontal fold ; a 

 long free horizontal fold rises close to the vertical plate, a little 

 below its upper extremity, revolving parallel with the whorl as 

 far as the aperture, when it unites with the ridge on the parietal 

 callus ; between these two folds sometimes occurs a very short, 

 free, horizontal fold ; (one immature specimen in my collection 

 possesses in addition an elongated denticle between this short 

 fold and the long upper fold). A very thin, free, horizontal fold 



Fig. 44. Plectopylis leiophis. 



Fig. 45. Plectopylis leiophis. 



Fig. 46. Plectopylis psettdophis. (, 

 original ; b and c, after Grodwin- 

 Austen.) 



rises below the vertical plate, running close to the lower suture 

 and terminating near the apertural ridge. 



The palatal armature consists of : first, a short thin horizontal 

 fold near the suture ; secondly, a longer horizontal fold, somewhat 

 deflected posteriorly, with an additional short wedge-like fold 

 attached to it, which has posteriorly, a little above it, a small 

 denticle ; thirdly, a shorter horizontal fold widened towards the 

 posterior extremity, then suddenly attenuated and indented, and 

 finally again widened a little ; fourthly, a short, slightly curved 

 horizontal fold, descending a little posteriorly, also slightly 



