196 MYRIST1CA. 



6. Cleidoth^erus. Deep valve attached, a bony appendage. 



Fig. 75, 76. 



7. Cumingia. Ligamentary pit in both valves, spoon-shaped. 



Fig. 87. 



MYOCHAMA. Stutch. (Mya and Chama.) Fam. Myaria, Lara. 

 — Descr. Inequivalve, irregular, attached, subequilateral; attached 

 valve flat, with two marginal, diverging teeth, and one end of a 

 little testaceous appendage fixed between them by a horny car- 

 tilage ; 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 impressions with a short sinus. — 06*. 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 appen- 

 dage bringing it near the Myariee. Fig. 73, M. anomioides. 



MYOCONCHA. Sow. (Mya and Concha.) Fam. Cardiacea, 

 Lam. — Deso-. Oval, equivalve, oblique ; urabones terminal ; 

 ventral margin rounded ; hinge with an external ligament, and 

 one oblique, elongated tooth in the left valve ; impression of the 

 mantle not sinuated. — Obs. The fossil genus has the general form 

 of Mytilus or Modiola, but the hinge of the Conchas generally. 



MYOPAKA. 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. 



MYMSTICA. Sw. A genus of « Pyrulinse,' ' Sw. thus described: 

 " Sub-pyriform ; spire strong, spiny, or tuberculated, nearly as 

 long as the base ; umbilicus either partially or entirely concealed ; 

 inner lip vitreous, thin ; the outer with an internal and ascending 

 canal ; the basal channel wide. Hippocastanea. En. M.432. f. 4. 



