68 NASSA. 
valve flat, with two marginal, diverging teeth, and one end of 
a little testaceous appendage fixed between them by a horny 
cartilage; free valve convex, with umbo incurved, and two very 
minute diverging teeth, between which the other end of the 
testaceous appendage is placed ; external surface of both valves 
conforming to the grooves or undulations of the shell to which 
the specimen is attached; muscular impressions two in each 
valve; palleal impression with a short sinus. Obs. This new 
genus, of which only one species is known, the M. anomioides 
from New South Wales, differs from Anomia and Anatina in 
being attached by the surface of one of the valves, from which 
circumstance the word Chama is added to its name: the little 
testaceous appendage bringing it near theMyarie. Fig. 73, M. 
anomioides. 
MY OCON’CHA. Sow. (Mya and Concha.) Fam. Cardiacea, 
Lam. Deser. Oval, equivalve, oblique ; umbones terminal; ven- 
tral margin rounded; hinge with an external ligament, and one 
oblique elongated tooth in the left valve; impression of the 
mantle not sinuated. Obs. This fossil genus has the general 
form of Mytilus or Modiola, but the hinge of the Conche gene- 
rally. 
MYOPARVA. Lea. (Myoparo, a piratical oar, galley.) Fam. Ar- 
cacea, Lam. A genus founded on a minute fossil bivalve shell, 
somewhat resembling Isocardia in form, but having a series of 
teeth placed on each side of the umbones. M. costatus, fig. 135. 
MYR'TEA. Turt. Venus spinifera, Auct. Lucina spinifera, 
nonnull. 
MYS’CA. Turt. A genus composed of species of Unio, Auct. 
which are distinguished by having “strong, transverse, notched, 
cardinal and long lateral teeth.’? Unio pictorum. 
MYTILA’CEA. Bl. The fourth family of Lamellibranchiata, Bl. 
containing the genera Mytilus and Pinna. 
MYTILA’CEA. Lam. A family belonging to the first section of 
the order Conchifera monomyaria, Lam. containing the genera 
Modiola, Mytilus, including Dreissina and Pinna. 
MY’TILUS. Linn. Fam. Mytilacea, Lam. Deser. Equivalve, cu- 
neiform, oblique, smooth, with umbones terminal, pointed, and 
posterior side broad, rounded; hinge linear, with a long, partly 
internal ligament; muscular impressions two in each valve; that 
on the posterior side large,irregular; that on the anterior, small; 
palleal impression irregular. Obs. The Linnean genus Mytilus in- 
cluded the Modiole, which differ from the Mytili in the rounded 
anterior side; and the Pinne, which are large shells, gaping at 
the posterior extremity. M. achatinus, fig. 158. 
NASSA. Lam. A genus of small shells united to Buccinum by 
some authors, but separated by others, on account of the little 
tooth-like projection terminating the columella. N. arcularia, 
fig. 423. 
