62 



PEOCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



In P. macrom'phalus, Blanf., belonging to tlie section Endothyra, 

 tlie anterior set of the palatal barriers is niuch simpler, being com- 

 posed of four short, broad, flattened, straight, horizontal folds, while 

 the posterior set consists of six narrow, horizontal lamellae, the fourth 

 and fifth being a little obliquely deflected posteriorly. The parietal 

 barriers again are much simpler than in P. woodthorpei, consisting 

 of a strong, vertical plate provided posteriorly at its lower extremity 

 with a minute denticle. 



P. laomontana, Pfr., from Laos, a member of the section Cherscecia, 

 is provided on the parietal wall with a single strong, lunate lamella, 

 its convex side facing the aperture and deflexed posteriorly below 

 (Fig. 1,6). On the palatal wall are found seven more or less hori- 

 zontal lamellae ; the second (from above) bifurcated posteriorly, 

 the sixth (which is very short) and the seventh (a little longer) have 

 each an elongated denticle posteriorly (Fig. 1, c). 



a be 



Tig. 1. — Plectopylis laomontana. 



P. hrachyplecta, Bens., a member of the section Endoplon, found 

 in Burma, has the palatal barriers in one series, the upper fold 

 being thin and horizontal; next come four short oblique folds, 

 nearly parallel, concave towards the aj)erture, and below these a short, 

 thin, horizontal fold near the lower suture ; the second fold has 

 a short, straight fold united to it posteriorly, while posteriorly 

 between the fifth and sixth folds occurs another short oblique lamella. 

 The parietal armature, on the other hand, consists of two strong, 

 vertical laminae, with short supports or ridges at the upper and lower 

 extremities ; a short, free, horizontal fold occurs below the vertical 

 plates. In another species of the section Endoplon, P. frangoisi, 

 H. Fisch., occurring in Tonkin (see Fig. 2), the palatal folds are also 

 six in number, the two upper and the basal one being horizontal, 

 rather long, while the third, fourth, and fifth are short, semicircular, 

 oblique, and a callous, transverse ridge connects the second, third, 

 fourth, and fifth. The parietal armature is composed of two strong, 

 obliquely divergent, transverse plates, with a short horizontal fold 

 above and a longer one below. 



In the section Ciiers^cia — a typical example being P. shanensis, 

 Stol. — the palatal barriers are- again in two series, the anterior set 

 comprising six thin, horizontal, subequal folds, while the posterior 

 series is composed of nine short denticles arranged in a vertical row. 

 The parietal armature consists of a strong, horizontal, median fold, 

 revolving over nearly half of the last whorl, and united to the 



