RECENT AND TERTIARY SPECIES OF LEDA AND NUCULA. 169 
§1. 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 1817. 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 Arcadas formed by these two genera, D’Orbigny 
describes only two species in his “Mollusques de Cuba;” viz., 
L. vitrea and L. jamaicensis, both of which have been found 
in the Gulf of Paria. The same author, in his “ Voyage 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 ground that 
