177 
NUCULA. Lamarck. 
Gen. Cuar. An equivalved inequilateral bivalve ; 
hinge with two interlocking rows of small teeth 
in each valve, diverging from a space within 
the beaks ; beaks conniving, turned back. 
Toisnevs’s Arca nucleus is the type of this Genus, which 
is well distinguished from other Arce by the disposition 
of the small interlocking teeth; several of the species have 
a concave space or tooth between the two rows of teeth, 
but as itis not constant to all the species naturally allied 
to the Genus Lamarck has omitted it in the generic cha- 
racter given in his Mémoire sur les fossiles des environs 
de Paris. 
NUCULA Cobboldiz. 
TAB. CLXXX.—Fig. 2. 
Spec. Cuar. 'Transverely obovate, convex; sur- 
face marked with zigzag furrows, diverging 
over the sides; edge entire. 
ae 
4 posterior side is very short ; the space between the 
rows of teeth is elongated, and very concave ; the inner 
surface is decorated with a coat of pearl; the outer sur- 
face is ornamented with numerous slight furrows, which 
are zigzag over the middle, and thence diverge on each 
side towards the front: it varies in gibbosity. 
I have met with three varieties of this ; the first a small 
gibbose one, was sent me from Holywells, by Mrs. Cob- 
bold ; a second, almost orbicular, was lent me by the 
