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 these 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 peristoine 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 



Fig. 78. Plectopylis repercussa. 



complicated, being of the same type as in Plectopylis Tcarenorum. 

 These two species, together with Plectopylis bensoni, P. anguina, 

 and P. linUrce, form a distinct group, connected with the group 

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

 horizontal median fold, given off 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 



