8 MOLLUSCA FROM THE CRAG. 



me for the purpose of being figured, are sufficiently characteristic to be fairly identified 

 with one of the recent British forms ; and I feel justified in assigning it to L. pcreyra. 

 This is also found at Stutton and Clacton, but I have only met there with the more 

 ovate and less elongated variety. 



.3. LiMNiEA TRUNCATULA (?) MiUL Tab. I, fig. 8, a — h. 

 BucciNUM TRUxcATULUM. MuU. Venn. p. 130, No. 325, 1774. 

 Helix fossaria. Mont. Test. Brit. p. 372, t. 16, fig. 9, 1803. 

 Lymxeus MiNUTUs. Brap. Moll. pi. 3, fig. 5-7, 1805. 



— rossARiDS. Turt. Man. fig. 108. 

 LiMNEA rossAKiA. FJem. Brit. An. p. 274, 1828. 

 LiMNEUs MINUTUS. Rossm. Icon. p. 100, t. 2, fig. 57, 1835. 



Z. Testa jjusiUd, ovato-cotiicd, perforata, tenui,fragili ; anfradibtis quinque convexis ; 

 mturis profundis ; spird elevatd ; apice acuto ; aperturd ovatd. 



Shell small, ovato-conical, perforated, thin, and fragile, with about five convex 

 volutions, and a deep suture ; spire elevated ; apex acute ; aperture ovate ; and a 

 slightly reflected pillar lip. 



Axis, \ of an inch. 



Locality. Mam. Crag, Bramerton. Recent, Britain. 



One small specimen, represented at fig. 8 h, sent to mc by Mr. Wigham for the 

 pur[3ose of description, appears to belong to this species ; it has the convex volutions, 

 deep suture, and open umbilicus, corresponding with those of the recent shell. Fig. 8 a 

 is the representation of a specimen from the cabinet of Mr. Lyell of a more doubtful 

 character ;* although more elongated than the general form of the recent species, it 

 appears to correspond in other respects, and I feel disposed to assign it to 

 L. truncatidus. This species is found in the truly Lacustrine beds of Stutton and 

 Clacton, corresponding precisely with the recent form. 



PLANORBis,f Midler, 1781. 



Gen. Char. Shell orbiculato-depressed, discoidal ; volutions apparent above and 

 below, convoluted upon a nearly horizontal axis, thin, light, smooth, and somewhat 

 corneous ; aperture simple, lunate, crescent-shaped, or subquadrate ; outer lip thin, 

 sharp ; inner lip slightly spreading over the body whorl. No operculum. 



The animals belonging to this genus are inhabitants of pure fresh water ; their 

 most favoured places of abode being in waters that are stagnant, although a few are 

 found in gentle streams ; but none are as yet kno\Mi in those places to which salt 

 or brackish water has access ; the specimens, therefore, found in the Crag must of 

 com'se have been accidentally introduced, and are few in number. Shells of this 

 genus are formed upon a nearly horizontal plane, and some considerable disagreement 



* Mr. Lj'ell's specinaen measures ^ of an inch, 

 f Etym. Planus, flat, and orbis, a circle. 



