HYDROBIA. 51 



Forth (Brown) ; Peterhead (Crombie, fide Macgillivray) . 

 West Indian. 



3. Rissoina decussata {Turbo decussatus, Mont.) =R. 

 pyramideUa, Brown : Weymouth (Bryer) ; Portobello 

 Sands (Laskey) ; Dunbar (Brown). West-Indian. 



4. Rissoina conifer a (Turbo coniferus, Mont.): Wey- 

 mouth (Bryer) ; north of France (De Gerville) . West- 

 Indian. 



5. Rissoina denticulata {Turbo denticulatus , Mont.) : 

 Weymouth (Bryer) ; Cornwall and Dunbar (Brown) ; 

 Herm (Lukis). West-Indian. 



The following are irrecognizable : — 1 . Rissoa sulcata, 

 Brown: Dunbar (Bingham). Apparently a Rissoina. 

 2. Rissoa Candida, Brown : " Belton Sands near Dun- 

 bar." Perhaps the same species as the last. 3. Rissoa 

 lactea, Brown (not of Michaud) : " Dunbar." Another 

 Rissoina, probably R. Chesnelii of Michaud, a native of 

 the West Indies and Mauritius. 



Genus IV. HYDROBIA. 

 (See vol. i. p. 63.) 



I would remind my readers that the chief characters 

 by which the present genus is distinguishable from Rissoa 

 (to which it is closely allied) consist in the foot of Hy- 

 drobia wanting the opercular appendage or caudal fila- 

 ment, and in Rissoa being truly marine, while this lives 

 in estuaries and brackish water only. In the latter 

 respect both genera may be regarded as the creatures of 

 habitat. Their shells are equally small. 



When I placed Hydrobia in the Paludinida, I had not 

 sufficiently considered its systematic relations. I now 

 withdraw it from that family. The description of the 

 operculum (vol. i. p. 55) must be amended by omitting 

 the words " or paucispiral." 



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