MOLLUSCA. G1 
differ greatly from one another and from the generi¢ char- 
acter. Some are found recent on our shores, while others 
occur only in a fossil state. Lamark, having rectified the 
Linnean character of the genus, has separated many species, 
now grouped, into distinct genera. In the restricted genus 
Anomia, the under valve has a hole or groove near the 
beak, which is closed by a testaceous operculum. This ap- 
pendage is fixed to rocks or stones, and has a ligament at- 
tached to it. 
In the genus Cranra, represented by the Anomia erano- 
laris of Linnzeus, the under valve is pierced by three holes, 
which are oblique and unequal. The genus GryPHaa was 
constituted from the Anomia Gryphus of Linnzus. The 
inferior valve is concave, terminating in a spirally involuted 
beak, projecting upwards ; the upper valve is small, and re- 
sembles a lid. A transversely striated pit at the hinge con- 
tains the ligament. The only recent species known is called 
G. angulata. Many species are found in a fossil state in 
the rocks of this country. 
Among the Anomia, Linnzeus placed the shells which 
compose the genus TEREBRATULA, the characters of which 
are so obvious and distinct. In this genus, which is inequi- 
valve and regular, the beak of the larger valve is produced, 
and pierced with a hole, through which the ligament of ad- 
hesion passes. [From the great extent of this genus in fossil 
species, several subdivisions have been proposed. 
From the Anomia placenta of Linnezeus, Lamark has form- 
ed his genus PLacuna. The hinge is remarkable for two 
teeth on the one valve, placed like the letter V, the base 
toward the beak, and two impressions on the other valve. 
It occurs in the Indian Seas. The natives polish it for or- 
naments. 
