46 RESEARCHES rPON THE HYDROBIIX.E 



Lingual dentition of i'. culminea, according to Troschel' : 

 E-hacliidian tooth very short and broad ; basal denticle with a 

 lobe or ridge connecting it with the lateral margin. Body of the 

 intermediate tooth longer than broad, and lunger than its pe- 

 duncle. Formula of the denticles : ^.^ - 9 - 19 - 25. 



Station, fresh water. 



Distribution, South America and the West Indies. 



Type P. Auheriana, D'Orbignt, in Sagra's Cuba, Moll., II, (1841) 8, pi. x, 

 fig. 6, 7. Hub. West Indies. 



The following are congeneric : — 



P. culminea, D'Oeb., Voy. Am. Merid., Moll., p. 386, pi. xlvii, fig. 10-12. 

 Bolivia. 



P. Cumingiana, D'Orb., Voy. Am. Merid., Moll., p. 385, pi. xlvii, fig. 14- 

 16. Chile. 



P. Parchappii, D'Okb., Voy. Am. Merid., Moll., p. 383, pi. xlviii, fig. 4-6. 

 Buenos Ayres. 



D'Orbigny's description of his genus Paludestrina would make 

 it include the entire subfamily Hydrobiinae, with the exception 

 of Stenothyra, and this was doubtless intended by him, as he 

 seems to have been ignorant of th,e generic names previously 

 proposed for the shells of the group. As in all such cases, we 

 must select a type from among the species described by him, and 

 of these we select the first, not only on account of the accordance 

 of such a selection with a rule of nomenclature generally adopted, 

 but because it will afford us a name for a group of American 

 forms which should be generically separated from the other 

 elongated fresh-water species which we have included in Bythi- 

 nella. 



The first species ever described by D'Orbigny, as far as we 

 have been able to ascertain, is the P. Auheriana of the " Mol- 

 lusques" of Sagra's Cuba. This species is said by the author to 

 be "common on the maritime sands of Cuba," which at once 

 suggests the idea that it may be a Hydrohia or Rissoa, and not 

 congeneric with the South American fresh-water forms we have 

 included in the genus, from one of which the lingual dentition of 

 the genus has been made out. But we find that Poey, an excel- 

 lent observer, has placed the P. Auheriana among ih^ fresh-water 



' Gebiss der Scliuecken, I, 108, pi. viii, fig. 5. 



