96 Mr. S. Stutchbury on two new genera of Mollusca. 
fact of the shells under notice being constantly attached, did there exist 
no other difference, would itself be a sufficient reason for regarding 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 
Myocnama.* 
Testa inequivalvis adherens. Valva affixa dentibus duobus margi- 
nalibus, divaricatis, ad umbonem disjunctis, foveold trigond interme- 
did alteram testacee appendicis extremitatem, cartilagine corned con- 
nexam, excipiente. Valva libera dentibus duobus inequalibus, 
parvis, divaricatis, alterd appendicis extremitate foveole intermedia 
ansertd. Umbones valve libere interne, alterius externée, recurvi. 
Impressiones musculares due, orbiculares, distantes, laterales. 
Impressio muscularis pallit 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 Cleidotherus 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 inz-_ 
quivalve, adhering ; the attached valve with two unequal diverging mar- 
ginal teeth, separated at the umbo bya 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 Myarie and Chamacee, 
