PLANORBIS. 93 



are connected together through the P. submarginatus of 

 Cristofori and Jan, alias the P. intermedius of Char- 

 pentier. Some of the aberrant forms are as difficult to 

 separate as those of P, spirorbis and P. vortex. The 

 present species was first made known by Lister. 



The P. turgidus described by me in the ^ Linnean 

 Transactions ^ is not a British species ; and I was mis- 

 informed as to the locality. Its nearest ally is, as I 

 stated, P. corneus ; but it has been erroneously referred 

 by subsequent writers to the present species. 



D. WhorJs rounded and not keeled. 

 10. P. cor'neus^, Linne. 



Helix cornea, Linn. Syst. Nat. ed. xii. p. 1243. P. corneus, F. & H. iv. 

 p. 147, pi. cxxvii. f. i-3. 



Body dark red or nearly black, of a greyish hue beneath, 

 with black and grey specks on the upper part : tentacles long 

 and curved, with rather blunt tips : eyes of a moderate size 

 and not prominent : foot slightly tubercled, narrow and angu- 

 lated in front, rounded and convex behind. 



Shell rather deeply concave above and nearly flat below, 

 somewhat solid and opaque, glossy, whitish-horncolour with 

 a reddish-brown tinge, closely but irregularly striate by the 

 curved lines of growth and marked with fine and close- set 

 spiral stria?, which are more perceptible in the first whorls ; 

 the upper surface is also sometimes pitted or impressed in an 

 irregularly quadrangular form like cut-glass : epidermis rather 

 thin : peripliery rounded and quite destitute of any keel or 

 angularity : wliorls b-Q, more perceptible on the umbilical or 

 lower side, in consequence of that part of the spire being 

 intorted ; diameter of the last whorl rather less than a third 

 of the whole shell ; they are very convex above and rather 

 compressed beneath : suture deep : mouth forming a segment of 

 two-thirds of a cii'cle : outer lip a little reflected, the upper 

 side not projecting much beyond the lower one : inner lip con- 



^ Horn-coloured. 



