b RESEARCHES UPON THE HYDROBIIX^ 



?ays that Ilartmann originally included but three species in hi> 

 genus, one of which was marine ; and rejects the name Ilydt^obia. 

 " because it had already been applied by Leach to a genus of in- 

 sects." But the name of the coleopteran genus is Hydrobius. 

 and suflBciently distinct to avoid confusion. Gray* gives the 

 Turbo vivas of Pennant, a marine species, as the type of the 

 genus Hydrobia, in which he is followed by Woodward^ and II. 

 & A. Adams.3 I shall therefore retain the name for the marine 

 species (included in Rissoa by Forbes & Hanley) until further 

 bibliographical researches can be made. That the marine, or 

 rather brackish-water forms truly belong to the same group with 

 the fresh-water species — the AmnicoliB, etc. — is evident from the 

 character of their lingual dentition, which I have recently ex- 

 amined in the Littorinella minuta (Cingula minuta, Gould) 

 of the coast of Massachusetts. The other characters of this 

 animal are also so similar to those of the fresh-water forms, both 

 in shell and soft parts, that it would, if found in fresh water, be 

 considered by many as an elongated Amnicola. The verge is 

 simple as in some of the fresh-water genera to be described below. 



In Sturm's " Fauna Deutschlands," Hartmann also published a 

 second genus under the name of Lithoglyphus (the MSS. name 

 of Muhlfeldt), which proves to belong to the Hydrobiinse, the 

 type being the Paludina naticoides of Ferussac, found in the 

 Danube. 



The small mollusks of the families Hydrobiinse and Pomati- I 

 opsinoe are not only numerous, but greatly diversified in form, in i 



the fresh waters of Xorth America. They may l)e distinguished I 



from all the rest of our fluviatile gasteropods, with some groups 

 of which they have often been confounded, by the presence of an 

 external verge, coexistent with a corneous subspiral operculum. 



Like the Yivipari and Alelaniie, they have recently received 

 considerable attention from American naturalists, particularly in 

 respect to their classification, which has been attempted upon 

 various grounds, but, as it would seem, with indifferent success. 

 In fact but little dependence can be placed upon the shell alone, 

 in the systematic .study of these groups ; the entire animal must 

 be examined for the discovery of the most important characters. 



• Turtoii's Manual, 2d ed., 1840, pp. 87, 88. 



* Manual of the Mollusca, p. 137. 



' Genera of Recent Mollusca, I, 335. 



