LYMN^CEA. 25 



Wernerian Mem., II, p. 524; Helix umbilicata, Pulteney, Cat. 

 Dorset, p. 47, pi. 20, f. 11 ; Helta; crasius, Da Costa, Brit. Sli., 

 p. 66, pi. 4, f. 11. 



Shell thick, depressed, of a brown horn-colour, sometimes 

 rufous or chestnut ; with five or six greatly compressed, equal 

 sized, compact, close-set volutions, the outer one rounded, the 

 others on the wider side rise nearly to an edge, and are divided 

 by a deep suture, having a subumbilicus in the centre ; upper 

 side largely and deeply umbilicated, exhibiting every volution, 

 spirally descending to the bottom ; aperture crescent-shaped, 

 compressed, and clasping the body volution. Diameter a quar- 

 ter of an inch ; and somewhat more than a tenth of an inch in 

 thickness. 



Common in ditches and stagnant pools in Great Britain and 

 Ireland. 



Genus IX.— SEGMENTINA.— Fleming. 



Shell divided internally by transverse septa into several 

 chambers, which communicate into each other by triradiated 

 apertures. 



1. Segmentina lineata, pi. IV, f. 3, 4. 



Segmentina lineata, Fleming, Brit. An., p. 279 ; lb., Ency. 

 Brit., pi. 367> f. 8; Planorhis nitidics, Miiller, II, p. 163; Dra- 

 pernaud, Moll., p. 46, pi. 2, f. 17> 18, 19; Rossmassler, Icon,, 

 II, p. 15, pi. 7, f. 114, 115; Brown, Illust. Conch., p. 33, pi. 

 14, f. 50, 51 ; lb., First Ed., pi. 41, f. 50, 51 ; Turton, Man., 

 p. 116, f. 91 ; Planorhis nautilexis, Fleming, Edin. Ency., VII, 

 p. Qd ; Kickx, Moll. Barb., p. 66 ; Planorhis lineakis, Alder, Mag. 

 Zool. and Bot., II, p. 114; Nautilus lacustris, Lightfoot, Phil. 

 Trans., XXVI, pi. 1, fig. 1, 2, 3, 4, 5, 6, 7 ; Montagu, Test. 

 Brit., p. 191> ph 6, f. 3; Hemithalamus lacustris, Leach, Moll., 

 p. 137 ; Helix lineata, Walker, Test. Min. Ear., pi. 1, f. 28. 



Shell compressed, subcarinated, extremely pellucid, smooth 

 and shining, horn-coloured, sometimes reddish-brown ; upper 

 surface convex ; apex depressed, concave, and deeply umbili- 

 cate ; with four volutions, the apical one lost in the depression, 

 the outer one very large, these are bordered on their outer 

 edge with a whitish spiral band, which terminates in the centre 

 at the junction of the volutions; outer volution exhibiting three 



E 



