114 MOLLUSCA. 
Mineral Conchology as occwring in a fossil state in Bri- 
tain. 
The patella unguis now ranks as a bivalve, and consti- 
tutes the genus Lineuxa in the acephalous family brachi- 
opoda of Lamark. Linneeus, who never saw more than one 
valve, placed it among the patella. Chemnitz, who ex- 
amined both valves, considered it as a pinna. These writ- 
ers had overlooked the figure of the perfect shell, with its 
tube or stalk, as given by Seba, vol. iii. fig. 16. No. 4. This 
specimen, which belonged to Seba, passed into the museum 
of the Stadtholder, and afterwards reached, in company with 
the spoils of the other Continental collections, the museum 
of Paris. Here Lamark examined it, and formed his new 
genus. And the same specimen enabled Cuvier to inves- 
tigate its anatomical structure, which he has explained in 
detail in the first volume of the Annales de Museum. Science, 
in this instance, as well as several others, profited by the 
successes of the late emperor of the French. This genus 
is destitute of a hinge. The valves are supported on a pe- 
duncle, and the shell is opened partly by the relaxation of 
the adductor muscle of the animal (and not by the external. 
membrane, as stated by Mr. Sowerby), and partly by the 
issuing forth of its spiral arms, which push asunder the 
valves like a wedge. 
Another genus was constituted and termed OrBicuLa, 
from the Patella anomala of Miiller, Zool. Dan. vol. i. p. 
14. t.5. The under valve is very thin, and fixed ; the up- 
per is orbicular, and depressed. It isa member of the same 
family as the preceding in the system of Lamark. 
32. Denrarium.—This very natural genus of Linnezeus 
has undergone no alterations, nor has our knowledge of the 
