58 CLASS I. TROPIOPODA. ORDER I. BIMUSCULOSA. 



CLEIDOTH.ER US, Stutchbury . 



Testa inaequivalvis, adherens; valva affixa convexissima, valva libera 

 plana ; dente cardinali conico, in fossulam valvse affixae inserto, 

 cum appendice testacea, elongata, recurva, ad cicatricem profundam 

 infra umbones cartilagine utrinque connexa. Impressio muscularis 

 pallii integra. Ligamentum externum. 



The genus Cleidothaerus, described by Sowerby in his ' Genera,' 

 offers another remarkable shell from the same locality as the former ; 

 and although differing considerably in general appearance, it will be 

 found to approximate to that of Myochama, both in having the testaceous 

 appendage, and in being always immediately fixed by the lower valve. 

 Deshayes informs us that this shell is the Chama albida of Lamarck, and 

 that the genus Cleidothaerus should be referred to the family of Chatnacea ; 

 there is, however, too clear an affinity in the clavicle or testaceous 

 appendage to the genera Myochama and Anatina, to question the pro- 

 priety of its arrangement with the Myaria. 



We adopt the well-known title, Cleidothaerus, of Stutchbury, as being 

 that by which this genus is generally known. De Roissy, who was the 

 first to notice a peculiarity in the general appearance of its shell, has a 

 prior claim to the name of Chamostrea ; but the discovery of the clavicle, 

 which is the most important feature, is due to Stutchbury. 



The shell of Cleidothaerus is described as being inequivalve, and some- 

 what pearly in the interior ; the attached valve is very convex, the other 

 flat, having a small pointed tooth fitting into a corresponding pit in the 

 former ; and there is a long, recurved, testaceous appendage, called the 

 clavicle, connected by a cartilage at both ends to a deep cicatrix under 

 each umbo. The muscular impression of the mantle is entire, and the 

 ligament is external. 



