94 CO^GBYLl A— DITHYRA 10. 



10. SPHENIA— TfJiJTOiV. 



Testa transversa, incequivalvis, incsquilateralis, latere antico hiante. 

 Cardo valves sinistrce dente elevato transversimdilatato,dextroe dente 

 concavo cum denticulo postico : lateralibus nullis. Ligamentum in- 

 turnum. 



Shell transverse, inec^uivalve, inequilateral, open at the anterior 

 end. Hinge of the left valve with an elevated transversely dila- 

 ted tooth, of the right valve with a concave tooth and small denti- 

 cle behind it : lateral teeth none. Ligament internal. 



This new and interesting genus, which in the Linn^an arrange- 

 ment would rank with the Mjre, 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 rocks 

 and the inside of dead bivalves. 



Binghami. SPHENiA testd cuneatd, dente concavo ohliqu^ inflexo . 



'■ Shell wedge- shaped, with the concave tooth oblique and inflected, 



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



