166 DESCRIPTION OF SHELLS. 
to be the same species ; but as intermediate forms occur, and they agree with the 
two varieties given by Deshayes, except in size, it is not desirable to separate 
them. 
Tellina craticula. (Tab. III. fig. 4.) 
Spec. Cuar.—Ovate orbicular, compressed, posteriorly pointed and obliquely 
truncated, ornamented with many concentric, erect, rather distant laminz ; 
beaks central; marginal fold small, near the hinge-slope. 
The more elevated and distant laminz and less-marked fold distinguish this 
shell from T. scalarioides of Lamarck, but they are so nearly alike, that Mr. Ed- 
wards is unwilling to consider them different ; and he may be right; but we are 
anxious to mark a difference between the English and French shells when it 
occurs, rather than hastily to unite them. 
Lucina serrata. (Tab. III. fig. 7.) 
Spec. Cuar.—Orbicular, with a rather straight hinge-line, convex ; surface 
ornamented with oblique doubly-arched strize which produce serratures on the 
superior margin; the two curves of the striz unite at a sharp angle rather 
nearest to the anterior margin of the shell ; lunette indistinct. 
Lucina serrata is one of several species belonging to a section of the genus 
which is distinguished by angularly bent concentric ridges. They have all 
usually been comprehended under the name Lucina divaricata. The fossil 
species are more numerous than the recent, of which there are however several, 
but all different from any of the fossil ones. The L. divaricata of ‘ Mineral Con- 
chology’ is not the same as any of the French species, unless it be the L. undu- 
lata of Lamarck, which Deshayes gives as only a variety. The species before 
us is the smallest known; it is well marked by the sharpness of the angle at 
which the two curves of the striz meet; in other species they are either joined 
by a short straight line or by a regular curve. 
We are indebted to the careful researches made by Mr. Edwards for this 
pretty little fossil. 
Fig. a, natural size. Fig. b, magnified. 
Lucina immersa. (Tab. III. fig. 24.) 
Spec. Cuar.—Subpentagonal, irregular, convex, smooth; lunette flat, lan- 
ceolate, sunk deep beneath the pointed beaks, which are curved forwards ; 
