CLASSES, ORDERS, ETC. 65 



large ; mouth oval, angulated above ; umbilicus none ; operculum 

 oval, angulated above, closely fitting. Length J inch. Streams, 

 ditches, canals. B. tentaculata. 



(b) Shell conoid, swollen towards the base, thin, subtransparent, 

 yellowish-horn coloured ; whorls four to five, tumid, separated 

 by a deep suture ; mouth nearly circular, less angulated above 

 than in B. tentaculata ; umbilicus small, distinct ; operculum nearly 

 circular. Length Jth inch. Ditches, cana's, and sluggish rivers. 

 More local than B. tentaculata. B. leachii. 



4. Paludestrina. Operculum horny, thin ; eyes placed on 

 tubercles. 



(a) Shell ovoid, subopaque, thin, yellowish-horn coloured; 

 whorls five to six, very convex; sutures deep and grooved; 

 umbilicus represented by a narrow chink ; mouth oval ; operculum 

 oval, nucleus lateral. In ditches between Greenwich and Wool- 

 wich which are flooded by the tide. P. similis. 



(b) Shell a lengthened cone, thin, glossy, yellowish-horn 

 coloured ; whorls six to seven, convex ; sutures not grooved ; mouth 

 oval ; umbilicus smaller than in P. similis. P. ventrosa? 1 



(c) Shell larger and more robust than P. ventrosa ; whorls six, 

 the last and penultimate whorl generally carinated ; suture not 

 channelled. Animal pale grey ; tentacles slender, not pointed at 

 ends, pale, not ringed ; eyes on dark coloured and not on pale 

 prominences ; sole of foot, transparent, pale, with a white stripe 

 down each side consisting of closely set whitish-brown specks. 

 Height fths inch. Plumstead marshes, and in a few other 

 localities. P. jenkinsi. 



Family III. Valvatidae. 

 Shell conoid, more or less depressed; mouth circular; oper- 



15 v. albida, white ; v. fulva, tawny, glossy ; v. ventricosa, more tumid, 

 globular- conical in shape, white ; v. zonata, reddish with one or more white 

 lines or bands ; v. prodncta, less tumid, in shape an elongated cone ; v. 

 excavata, whorls more rounded, suture much deeper ; m. decollatum, with the 

 apex decollated ; v. pallida, shell very pale horn-coloured ; m. scalariforme, spke 

 scalaria. 



16 v. albida, white; v. elongata, smaller, spire more produced. 



17 v. pellucida, clear white, nearly transparent; v. minor, smaller, spire 

 shorter ; m. decollatum, spire decollated, 



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