1 14 MOLLUSCA. 



Mineral Concholoyy as occurring in a fossil state in Bri- 

 tain. 



The patella unguis now ranks as a bivalve, and consti- 

 tutes the genus LINGULA in the acephalous family brachi- 

 opoda of Lamark. Linnaeus, who never saw more than one 

 valve, placed it among the patellae. 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 ORBICUL.A, 

 from the Patella anomala of Miiller, ZooL Dan. vol. i. p. 

 1 4. t. 5. The under valve is very thin, and fixed ; the up- 

 per is orbicular, and depressed. It is a member of the same 

 timiily as the preceding in the system of Lamark. 



32. DENTALIUM. This very natural genus of Linnaeus 

 has undergone no alterations, nor has our knowledge of the 



