TO GEOLOGY. 79 
rather deep ; marginal teeth small on the basal margin— 
larger anteriorly and posteriorly. 
Diam. .2, Length 7-20ths, Breadth 7-20ths, of an inch. 
Observations. This very curious and interesting species 
is remarkable for its obliquity and the sculptured grooves of 
its folds. At first sight it might be mistaken for the genus 
Lima. The seat of the ligament is impressed, and forms a 
small pit immediately below the point of the beak. 
The genus Pectunculus has been found in England as low 
in the series as the Great Oolite and as high as the Crag. 
Mr Sowerby describes five in the London Clay. In the 
Tertiary Tables of M. Deshayes, we find twenty-seven 
species almost equally distributed over the three periods— 
there being thirteen species in the Pliocene, eighteen in 
the Miocene, and nineteen in the Eocene. In the Green 
Sand of New Jersey, Dr Morton has obtained casts of 
this genus. In the Tertiary of Maryland Mr Say has 
observed one species. Mr Conrad has described three spe- 
cies from the Tertiary of Claiborne and observed one other, 
the pulvinatus of Lamarck, near York Town, Virginia. 
GENUS NUCULA. Lamarck. 
NM. Sedgewickii. Plate 3. Fig. 58. 
Description. Shell ovately elliptical, oblique, subangular 
behind, inflated, very inequilateral, smooth ; swollen over 
