THE LAND AND FRESHWATER MOLLTJSCA OF DORSETSHIRE. 87 



ORDER II. PUXMONOBKANCHIATA. 

 FAMILY LIMN^ID^E. 



Genus T.PLANORBIS, Guettard. 



1. PLANORBIS NITIDUS, Midler, pi. 6. 



HELIX FONTANA, Mont. Test. Brit., vol. ii., p. 462, pi. 6, f. 6, 

 Pult. cat., Rack, ed., p. 53, pi. 19, fig. 19. 



Shell slightly convex above, very thin, glossy and prismatic, pale 

 yellowish horn-colour or whitish ; whorls four to five, broadly over- 

 lapping one another, the last forming the greater part of the 

 shell ; periphery rather sharply keeled ; umbilicus small, not deep. 

 L.0.06. B.0.225. 



Hab. Ponds, marshes, and stagnant water. Ditches about 

 Wareham (Montagu) ; Chamberlayne's meadows, Bere Regis 

 (J.C.M.P.). 



2. p. NAUTILEUS, Linn., pi. 6. 



TURBO NAUTILEUS, Pult. cat., Hack, ed., p. 50, pi. 19, fig. 16- 

 Robinson's Isle ofPurbeck, p. 178. 



Shell flat, very slightly concave above, convex below, thin, nearly 

 smooth, light brown or white; periphery slightly and bluntly 

 keeled ; whorls three, the last broad and dilated, larger tlian the 

 rest of the shell, with ridges often spined; outer lip thin, often form- 

 ing a perfect peristorae with the inner lip; umbilicus deep and 

 wide. L.0.035. B.O.I. 



Hab. Lakes, ponds and ditches ; it is a British Tertiary 

 fossil. Ditches, Stoborough meadows, Wareham ; water 

 courses, Sturminster Marshall (J.C.M.P.) ; pools, Chapman's 

 Pool, near Encom.be ; Newton Manor. Swanage . (Smith) ; 

 Lulworth, between Castle Gate and Arish Mill (Daniel). 



3. P. ALBUS, Milller, pi. 6. 



HELIX ALBA, Pult. cat., Rack, ed., p. 53, pi. 19, f. 18. 



Shell flat above, with a shallow umbilical depression, thin whitish- 

 grey, with very fine closely-set longitudinal striae, which are distinct 

 in young specimens, and scarcely perceptible in adults ; epidermis 

 thick, often clothed with fine bristles ; periphery slightly compressed, 

 having a faint trace of a keel ; whorls five, slightly overlapping 

 each other, and increasing rapidly, the last being the largest; 

 inner lip continuous with the outer iip, which is slightly reflected. 

 JL.0.08. B.0.275. 



Hab. On aquatic plants in marshes, ponds and ditches. 

 Generally distributed. 



