PLECTOPTLIB, 



139 



Hah. Burma: Mergui (PJiilippi); Moulmain (StoliczJca, Theo- 

 bald, Fea); Nattoung (Theobald); Pha-thinz (Eungerford). 



The name Helix adiatina having previously been employed 

 (Potiez & Miehaud, Galerie de Douai, i, 1838, p. G8), it is neces- 

 sary to apply another designation to the shell hitherto known as 

 Plectopylis achat'ina, and I have much pleasure in associating with 

 it the name of the naturalist wTio created the genus Plectopylis. 



The shell is sinistrorse, disk-shaped, very widely umbiUcated, of 

 various shades of chestnut, usually paler and sometimes flammu- 

 lated below, irregularly and finely striated. The apex is usually, 

 but not invariably, raised shghtly above the plane of the whorls. 

 There are six or six and a half whorls, which increase gradually, 

 and are more or less flattened above and tumid below ; the first 

 three and a half are smooth or nearly so, while the next two are 



Fig. 70. — Plcctopi/lis bensoni. 



somewhat coarsely striated and strongly decussated by spiral 

 lines, less distinct on the upper side of the last whorl, obsolete at 

 its side, but reappearing in the umbilical region. The last whorl 

 is bluntly keeled above and subangulated at the periphery ; this 

 whorl suddenly widens at the aperture w-here it is deeply 

 deflected. The aperture is almost horizontal, elliptic cordate, 

 while the peristome is thickened and strongly reflected, livid or 

 purplish-brown in colour, never ivhite; the margins are united by 

 a raised sinuous ridge, slightly notched at the junctions above 

 and below. The parietal armature is of the same type as that of 

 F. repercussa, but the loiver arm of the bifurcation is the longer of 

 the two (see fig. 70 c, which shows part of the parietal wall with 

 tlie posterior portion of its armature), and the lower free hori- 

 zontal fold close to the lower suture does not reach as far as the 

 apertural ridge, and does not extend beyond the loiver arm of the 

 bifurcation and its posterior supjwrt. Y\g. 70 a gives the anterior 



