163 
described six recent and tbe same number of fossil species ; Sow- 
erby four fossil and one recent ; Defrance enumerates twelve fossil, 
and we have published two recent and two fossil species. Of all 
these the tellinoides, Sowerby, and lanceolata, Lam., appear to be 
the largest. 
The inhabitants are thus described by Blainville : body subtri- 
quetrous ; mantle open on its inferior half only, the margins entire, 
denticulated on the whole length of the back, without posterior 
elongations ; foot very large, thin at its origin, dilated in a large 
oval disk, the margins of which are furnished with tentacular digi- 
tations ; anterior buccal appendices very long, pointed, rigid, and 
applied against each other like a kind of jaws; the posteriors 
equally rigid, and vertical. 
Nucula limatula. — Specific character. Oblong-ovate, ros- 
trated, pellucid ; beaks subcentral, not elevated ; margin entire. 
Desc. Shell transversely elongated subovate, green olive, nearly 
pellucid, smooth, polished, with slight indulations of increment : 
beaks not prominent above the curve of the hinge margin ; hinge 
margin anteriorly abruptly compressed ; the compression not reach- 
ing the tip ; rectilinear nearly to the tip which is a little recurved ; 
posteriorly almost regularly, but obtusely arquated : posterior mar- 
gin regularly rounded : anterior margin somewhat rostrated, not 
truncated : within a little perlaceous : margin entire : line of the 
teeth slightly interrupted and a little angulated at the fosset, ex- 
tending more than two thirds of the length of the shell, rectilinear 
before and behind : teeth prominent, numerous, acute, much angu- 
lated at their bases and longer than the breadth of their bases : 
fosset triangular, short, rather small, and but little oblique. 
This pretty species was presented to me by Nuttall as having 
been taken from the stomach of a fish at Nahant, Massachu- 
setts. 
It resembles the N. fiuviatilis, Schroter, and the iV. rostrata^ 
Montague, but the rostrum is not truncated, and the summit is more 
central than in those species. It is still more closely related to N. 
laevis, nob., but it is proportionably a little longer, and in that spe- 
cies the posterior series of teeth is a little arquated', and the com- 
pressed anterior hinge margin extends quite to the tip. I must 
say, however, that I have seen but a single specimen, and but a 
single valve of the present shell. The N. arctica^ Grray, which 
