210 



another is observable : at nearly equal distances, four or five rugae are 

 disposed, as if the consequence of different periods of growth. 



On viewing the different specimens of ostracites and gryphites, in my 

 collection, I cannot help doubting as to the propriety of the formation 

 of a distinct genus for this shell. I there find specimens in which the 

 beak and the body of the valve possess various degrees of curvature, in a 

 series of gradation, from the complete curve of the gryphites to the slight 

 turn of the edible oyster. , 



CXXXVII. Ostrea. A rough adherent inequivalved bivalve ; the hinge 

 without a tooth. The pit of the hinge increasing with age, in the larger 

 valve. The cartilage, half internal. One muscular impression. 



The genus Ostrea, of Linnaeus, was doubtlessly much confused, he 

 having introduced in it several shells, which, like the Pectens, had a full 

 claim to a distinct genus. Bruguiere very properly separated from this 

 genus the genera Pecten and Ptrna, and introduced into it several shells 

 really belonging to this genus, but which had been placed by Linnseus in 

 the genus Mytilus. Lamarck proceeded still further, and seems to have 

 reduced this genus within its proper limits, by withdrawing from it those 

 shells with which he has constituted the genera Vulsella and Gryphea. 



Lamarck describes eighteen species of this genus, as found fossil in the 

 environs of Paris : O. bellovacina, O. hippopus, O. deltoidea, O. bimmculata, 

 O. vesicularis, O. pseudo-chama, 0. linguatula, O. cochleariu, O. longirostris, 

 O. canalis, O. crenulata, O. cyathula, O. spathulata, O. deformis, O. uncinata, 

 Q.flabdlula, O. cymbula, O. pectinata. 



Several species of this genus are also found in different parts of the 

 continent, as well as of this island. 



The most extraordinary shell of this genus, for size, is the large fossil 

 oyster, the recent analogue of which, from Virginia, appears to be de- 

 picted by Lister, Hist. Conch. PL 200, Fig. 34, and PL 201, Fig. 35. It 

 is chiefly found at Heutlingen and Aristorf, in Switzerland. The shell of 

 this ovster is sometimes from two inches to two inches and a half in thick- 



