90 Bulletin 35 238 



Page 169 



Preliminary Observations. 



The genus Nucula was created by Lamarck in 1799, for 

 small bivalve shells having a nacreous interior and a line of 

 numerous hinge-teeth interrupted beneath the umbo by a pit 

 for the insertion of the ligamental cartilage. The few species 

 known to Linne were included in his genus Area. The 

 genus Leda is ascribed to Schumacher, who published the 

 name in 1S17. But it was not until some twenty or thirty 

 years ago that the name was generally adopted for the 

 rostrated species formerly included in Nucula. Of the little 

 group of Arcadse formed by these two genera, D'Orbigny 

 describes only two species in his " Mollusques de Cuba ;" viz., 

 L. vitrca and L. Jamaieensis, both of which have been found 

 in the Gulf of Paria. The same author, in his "Vo)^age dans 

 l'Amerique Meridionale, " mentions nine species of Leda and 

 five of Nucula. Of these, Nucula semiornata and Leda 

 patagonica (the latter now recorded from the Gulf of Paria), 

 are the only ones named from the eastern side of the South 

 American continent, the other twelve being all west coast 

 shells, and apparently different from any Westindian or 

 Brazilian species. Hanley gives two species as Westindian 

 (Recent Bivalves, 1843-56), one being the Nucula tellinoides 

 said to have been found at Cumana, and the other the 

 N. recurva of Conrad, neither of which has occurred to me. 

 Krebs, in his list of the Westindian Molluska (1864) does 

 not name any species of the group. 



Other general observations on the Molluska treated of in 

 this communication will be found prefixed to the descriptions 

 in each of the following sections : it is only necessary here 

 for me to express the hope that the roughness of the accom- 

 panying illustrations will be pardoned on the gronnd that 



