104 HELICIDJB. 



flattened, apex a little raised. Whorls six to seven, increasing 

 slowly and regularly, flattened above, rounded below, the last 

 angulated above the periphery and round the umbilicus, and 

 descending shortly and abruptly in front. Aperture heart-shaped ; 

 peristome white, scarcely thickened, a little reflected ; the mar- 

 gins united by an elevated sinuous ridge on the parietal callus, 

 notched at the lower junction. Umbilicus wide and deep. Parietal 

 wall with a thin vertical plate, strongly deflected posteriorly 

 below, and giving off a short horizontal ridge at the upper 

 extremity on each side ; a long horizontal flexuous fold rises 

 close to the upper extremity of this plate on the anterior side, 

 descending suddenly at first, then ascending gradually, and after- 

 wards gradually descending, following the deflection of the last 

 whorl, becoming united to the ridge at the aperture ; a second, 

 shorter, horizontal fold occurs below this one, rising close to the 



Fig. 48. Plectopylis perrieres. 



lower extremity of the vertical plate, proceeding horizontally at 

 first, and then ascending a little; another very thin fold rises 

 below the vertical plate, running parallel to the lower suture as 

 far as the aperture, where it unites with the ridge. Palatal folds, 

 five ; the first, rather long and thin, near to and parallel with the 

 suture, with a deep indentation near the posterior extremity, 

 dividing it into two unequal parts ; the second, horizontal, a little 

 deflected posteriorly, with an elongated denticle posteriorly, and a 

 second, smaller, one above the first ; the third fold much shorter, 

 strongly curved downwards posteriorly, with a minute denticle 

 posteriorly ; the fourth fold vertical with an obliquely descending 

 ridge posteriorly at the upper extremity, and bifurcated at the 

 lower extremity, the anterior arm of the bifurcation the shorter ; 

 a minute denticle occurs near the ridge at the upper extremity 

 and a second one near the middle, both on the posterior side ; 

 the fifth fold is thin, horizontal, and strongly deflected on both 

 sides." (Gude.) 



