96 Mr. S. Stutchbury wi two new genera of MoUnsca, 



fact of the shells under notice being constantly attached, did there exist 

 no other difference, would itself be a sufficient reason for reaardins them 

 as distinct from Anatina. Under these circumstances, I have thrown to- 

 gether such observations as will point out their distinguishing peculiarities 

 until further information may confirm the propriety of continuing them as 

 genera, or enable us to ascertain their true affinities, and correct situation 

 in the system. The first I propose to call 



MyOCHAMA.* 



Testa incequivalvis adhcerens. Valva affixa dentibus duobiis margi- 

 nalibus, divaricatis, ad umbonem disjunctis, foveold trigond interme- 

 dia alteram testacece appendicis extremitatem, cartilagine corned con- 

 nexam, excipiente. Valva libera dentibus duobus incequalibus, 

 parvis, divaricatis, altera appendicis extremitate foveolce intermedicB 

 insertd. Umbones valves libera intern^, alterius externe, recurvi. 

 Impressiones musculares dues, orbiculares, distantes, laterales. 

 Impressio muscularis pallii sinu brevi, lato. Ligamentum tenue, 

 externum. 



At first sight this shell might be passed over as an Anomia, but it may 

 readily be distinguished by examining the attached valve, which will 

 be found to be destitute of the foramen ; from Cleidothaerus it differs 

 in wanting the conical tooth of the hinge, as well as in the shape of the 

 muscular impressions, in having a sinus in the muscular impression of 

 the mantle, and in the attached valve being the smaller. The following 

 characters will at once distinguish it from every other genus. Shell inae- 

 quivalve, adhering ; the attached valve with two unequal diverging mar- 

 ginal teeth, separated at the umbo by a triangular pit, in which one end 

 of a testaceous appendage is inserted and connected by a horny cartilage ; 

 the free valve with two unequal, small diverging teeth, close under the 

 umbo, in which is inserted the other end of the testaceous appendage. 

 The umbo of the free valve is curved inwards, that of the fixed valve 

 outwards. Muscular impressions two, nearly orbicular, distant, lateral. 

 There is a short broad sinus in the muscular impression of the mantle. 



* From the circumstance of the Shell thus named connecting in itself some 

 of the characters of the Myariae and Chamacea:. 



