338 HENKY CLIFDKN BUU'NUF. 



aperture as the basal fold, and running parallel to it ; (c) one 

 on the parietal wall, very wide, very strong, strengthening in 

 its advance inwards, flat, angled above and below, scarcely 

 paler than the rest of the shell, and set further back from 

 the aperture than the other two. 



Height about 0'85 to 0"95, width about 1'80 to 1*95 nun. 



Hab. — Fern Kloof, Grahamstown (J. Farquhar). 



The type, in the British Museum, not being available to me 

 for exact measurement, the dimensions given above are to be 

 taken as a fair average, ascertained from other adult examples 

 collected by Mr. Farquhar at the same locality as the type. 



The folds on the outer and basal walls, being solid, show no 

 corresponding sulci on tlie outside, where, however, their posi- 

 tions may be seen through the semi-ti'ansparent shell. Each 

 appears as two little pale bands nearly parallel, separated by 

 a dark space and converging towards the ends, suggesting 

 the presence of a groove on the outside of the shell. The 

 reason for this complex appearance seems to be that the light, 

 entering the thin, translucent shell from all sides, is strongly 

 reflected from the polished exterior of the folds, thence show- 

 ing, through the shell, as the pale bands • but, as it cannot 

 escape through their solid centres, the dark spaces there 

 intervene. 



In well-matured specimens none of the folds can be clearly, 

 if at all, discerned through the aperture before breaking 

 away part of the outer wall, but, in younger shells, those on 

 the outer and basal walls can be traced indistinctly. 



The shell, with part of the outer wall broken away to show 

 the internal folds, depicted in fig. 5, Avas, before being broken, 

 carefully compared with the type by Mr. Ponsonby and found 

 to correspond in every way. 



Fig. 6 shows a shell Avith about half of the last whorl, and 

 with it the lamella on the outer and basal walls, removed, 

 exposing the parietal lamella in its full development. 



Although this species is widely excavated and is furnished 

 with three internal lamella, it cannot well be mistaken for 

 trilamellaris, from which it differs in the following con- 



