PLANORBIS. 151 



Shell small, pale olivaceous horn-coloured, depressed, 

 about three or four times as broad as high, very thin and 

 semitransparent, glossy. Both disks, the left more par- 

 ticularly, moderately concave in the middle, the apex rather 

 abruptly sunken. Whorls about four, very deeply divided, 

 rounded, somewhat projectingly so upon the right disk, 

 where the inner slope is much more abrupt, of fast in- 

 crease, smooth, or at most only slightly wrinkled across. 

 Body about as broad as high, equally wide on both disks ; 

 well rounded at the periphery, the slopes tolerably even, 

 the lower, if anything, rather shorter and less convex. 

 Mouth as in albus. Diameter two lines. 



Mr. Jeffreys having forwarded to us examples of his 

 P. glaber, and the characteristics of the species, agreeing 

 with his published account of the distinctive features be- 

 tween it and albus, we are compelled to adopt the prior 

 appellation. The P. Icvvis was published as new, because 

 the specimen of P. glaber given to Mr. Alder by the author 

 of the species, proved to be a variety of albus. 



The animal is grey, dark about the head and sides of the 

 neck, with pale tentacula, and a rather large foot for its 

 size. Mr. Spence Bate has observed that the teeth have 

 more strongly serrated margins to their hooks than those 

 of albus. 



This shell is local. It occurs near Penzance (R. T. Mil- 

 let) ; near Falmouth (Cocks) ; in Staffordshire and So- 

 mersetshire, and in marshes on the sea-coast near Swansea, 

 Cardiff, and Manorbeer, in Pembrokeshire (Jeffreys) ; in 

 ponds at Whitley Quarries, and on Holy Island, North- 

 umberland (Alder). In Ireland it occurs near Belfast (W. 

 Thompson) ; and at Cork (J. D. Humphreys). 



