36 eO^CRYLW—DlTHYRA. 10. 



10. SPHEmA—TURTON. 



Testa transversa, inaquivalvis, ineequilateralis, latere antico 

 hiante. Cardo valca; sinistra dente elevato iransversim 

 dilatato, dextrte dente concavo cum dent iculo post ico : latera- 

 libus nullis. Ligamentum internum. 



Shell transverse, inequivalve, inequilateral, open at the anterior 

 end. Hinge of the left valve with an elevated transversely 

 dilated tooth, of the right valve with a concave tooth and 

 small denticle behind it : lateral teeth none. Lijiament 

 internal. 



This new and interesting genus, which in the Linneau arrange- 

 ment would rank with the MyjB, is sufficiently defined by its own 

 fixed and peculiar characters. 



From the Mya it differs, in having the valve which contains 

 the tooth smaller, and received within the opposite one ; in being 

 closed at the hinder extremity; and in being furnished with a 

 concave tooth in the larger valve, behind which is a small 

 denticle. The valves are also very unequal. 



And from the Corbula, in having the tooth of the left valve flat 

 and transversely extended^ with the anterior extremity a little 

 open. 



The outline is subject to some variation ; but all of them have 

 a flattish or wedge-shaped form : and inhabit the interior of 

 rpcks, and the inside of dead bivalves. 



:^inghami. SpHENiA testd cuncatd, dente concavo oblique injlexo. 



* Shell wedge-shaped, with the concave tooth oblique and inflected, . 

 Tab. nost. 3, fig. 4 and 5, and 19, fig. 3., 



