90 
Bulletin 35 
238 
Page i6g 
Preliminary Observations. 
The genus Niicula 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 1817. But it was not until some twent}’ or thirty 
years ago that the name was generally adopted for the 
rostrated species formerly included in Nucula. Of the little 
group of Arcadae formed by these two genera, D’Orbigny 
describes onh' two speciesinhis “Mollusques de Cuba viz., 
L. vitrea and L. janiaieensis, both of which have been found 
in the Gulf of Paria. The same author, in his “Vojmge dans 
I’Amerique Meridionale,” mentions nine .species of Leda and 
five of Nucula. Of these, Nucula seniiornata and Leda 
patagonica (the latter now recorded from the Gulf of Paria), 
are the only ones named from the ea.stern side of the South 
American continent, the other twelve being all we.st coast 
shells, and apparently different from any Westindiau or 
Brazilian species. Hanley gives two species as Westindiau 
(Recent Bivalves, 1843-56), one being the Nitcula tellinoides 
said to have been found at Cumaua, and the other the 
N. recurva of Conrad, neither of which has occurred to me. 
Krebs, in his list of the Westindiau Molluska (1864) does 
not name an}' 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 nece.ssary here 
for me to express the hope that the roughness of the accom- 
panying illustrations will be pardoned on the ground that 
