Mr. H. E. Strickland ofi the (/enus Cavdhna. 101 



Astarte. In front of the hinge is a deep and distinct luniile. The 

 lateral teeth are remote and very strong ; the anterior one of the 

 right valve obtusely conical, the posterior one of the left valve 

 elongated, and both mutually entering deep pits in the opposite 

 valves. Umbones approximate. Muscular impressions very deep, 

 placed immediately below the lateral teeth, their surfaces smooth ; 

 the posterior impression round, the anterior one ovate. Above 

 the latter in both valves is a small oval detached muscular im- 

 pression placed on the hinder surface of the lateral tooth, for the 

 insertion of the retractor muscle of the foot. Pallial impression 

 entire, parallel to the margin, which is not crenated. External 

 surface of the shell more or less irregularly imbricated by the 

 lines of growth. The geographical distribution of this genus is 

 as yet confined to Northern Europe ; its geological range is from 

 the base of the lias up to the inferior oolite. 



Several species of this genus were described by Sowerby in his 

 ' Mineral Conchology,' under the genus Unio. They differ how- 

 ever from the whole of the Unionidce in many respects, especially 

 in the want of the small accessory muscular impression behind 

 the anterior one (which occurs in the Unionidce, and to which a 

 branch of the retractor muscle of the foot is attached), in the 

 presence of the lunule, in the shell not being nacreous, and in the 

 habitat having been marine, as is sufficiently proved by the other 

 fossil animals whose remains invariably accompany these shells. 

 M. Goldfuss has been no more successful than Mr. Sowerby 

 in detecting the true generic relations of these shells, having in 

 his ' Petrefacten^ referred different species of them to the genera 

 Unio, Cijtherea and Lucina, without detecting the essential cha- 

 racters which distinguish them from all these genera. 



M. Agassiz was the first to combine the different species of 

 this gi'oup into one genus, though he failed to perceive that they 

 are much more closely allied to the Venerida than to the Unionidce. 

 To this genus he gave the name of Cardinia in a paper read to the 

 Helvetic Society at their meeting at Basle in 1838, and in 1840 

 he published the characters of the genus in his translation of 

 Sowerby's ' Mineral Conchology.^ In 1840 Mr. J. E. Gray gave 

 the name Ginorga to this genus in the ' Synopsis of the British 

 Museum,' p. 154; but this mere name, destitute alike of ety- 

 mology and of definition, can luve no claim for adoption. In 

 January 1841, M. de Christol defined a genus Sinemuria in the 

 ' Bulletin de la Societe Geologique de la France,' which from the 

 characters assigned is evidently identical with the genus before us, 

 though he errs in supposing the ligament to have been internal 

 instead of external. Lastly, in March 1842 jMr. S. Stutchbury 

 described this group in great detail in the ' Annals of Natural 

 History,' and bestowed on it the name of Pnchyodon, a name 



