PLECTOPYLIS. 



147 



obsolete at the side, but reappearing in the umbilical region. 

 The spire is a little raised, the suture linear. There are seven 

 regularly coiled whorls, which increase slowly and gradually, and 

 are flattened above and tumid below. The last whorl is tri- 

 carinated, one keel being at the periphery, one above, and another 

 below (in young shells tliese keels are provided with a fringe of 

 coarse hairs) ; this whorl widens suddenly at the aperture, where 

 it is deeply deflected. The aperture is almost horizontal, elliptic 

 cordate ; the peristome white, thickened, and strongly reflected ; 

 the margins united by a raised flexuous ridge, slightly notched 

 above and below at the junctions. The parietal armature is very 



wm 1 



Fig. 78. — Plectopylis repcrcussa. 



complicated, being of the same type as in Plecto/)ijlis Icarcnovmn. 

 These two species, together with PJectojiijlis bensoni, P. aiKjulaa, 

 and P. Uutero', form a distinct group, connected with the group 

 of P. ponsonhiji by a transition form, P. cairnsi. A long, stout, 

 horizontal median fold, given ott' at the apertural ridge, proceeds 

 parallel with the last whorl for a quarter of the length of that 

 whorl, when it gives off a shortly descending, slightly reflected 



l2 



