166 LITTORINID.E. 



the basal level, the upper disk merely convex, the lower 

 area much roundetl, but not produced. It is rather thin, 

 semitransparent, pure white, highly polished, and perfectly 

 smooth, excepting at the mouth of the umbilicus, which is 

 furnished with bluntly rounded spiral costellaj that are 

 divided from each other by well-marked sulci. There are 

 three subcylindraceous whorls that are much less convex 

 above, but neither flattened nor sunken at the suture. The 

 spire is scarcely raised ; the two first volutions, of which 

 the apical one is blunt and almost level, are short, and of 

 slow increase ; the body is ample ; its suture is rendered 

 very distinct by the somewhat abrupt rise of the succeed- 

 ing whorl. The umbilical opening is large, and its cavity 

 deep. The aperture is almost orbicular, about as high as 

 broad, and occupies two-thirds of the entire length, and 

 about one half the basal diameter of the shell. The peri- 

 stome is continuous, but is only attached to the body by a 

 narrow strip. Both lips are acute, and greatly arched ; 

 the outer one is not expanded, except, perhaps, at the 

 base ; the pillar-lip is elevated, a little reflected, and longi- 

 tudinally wrinkled on its internal surface. 



Two very minute specimens were forwarded to us along 

 with Marg. pusilla by Mr. Jeff*reys, and a larger one, 

 which measured rather more than a line in breadth, and 

 about three-sevenths of a line in length, was transmitted to 

 us, as deserving our attention, by Mr. Alder of Newcastle- 

 on-Tyne, after whom, in the event of their not proving to 

 be the foreign species, we have doubtfully referred them 

 to, w^e would suggest they should be named. They were 

 dredged by Mr. Barlee, but he had not preserved their 

 localitv. 



