80 CONTRIBUTIONS 
the umbones; substance of the shell thick ; lunule none ; 
beaks elevated, recurved; anterior series of teeth short— 
posterior series long ; fosset small and oblique ; cavity of 
the shell rather deep; margin very minutely crenulate ; 
nacre very pearly. 
Diam. .4, Length .6, Breadth .8, of an inch. 
Observations. Resembles Gobboldie and laevigata (Sow- 
erby). Itdiffers from the first in being smooth—from the last 
in not being truncate, and from both in having a crenulated _ 
margin. It has perhaps a stronger resemblance to the mar- 
garitacea of Lamarck, a recent European species, and the 
only recent one known to be crenulate. That distinguished 
naturalist says it is found fossil in various parts of France. 
It appears to me that our shell differs in being more 
robust, more transverse, and having less pointed teeth. 
In fine specimens of the Sedgewickii, with the aid of the 
microscope, minute diverging lines may be observed. 
In attaching the name of a distinguished geologist to 
this species, 1 must make my acknowledgements for the 
instruction and pleasure derived from his eminently useful 
labours. 
MN. ovula. Plate 3. Fig. 59. 
Description. Shell ovate, oblique, inflated, very inequi- 
lateral, transversely striate, longitudinally and very mi- 
nutely ribbed ; substance of the shell thin ; lunule large, 
not deeply impressed ; beaks pointed, recurved ; anterior 
series of teeth short—posterior series long ; fosset nearly 
2 
