MYARIA. 195 



into two kinds : 1st. Monomyaria, those which have but one 

 adductor muscle, and consequently have but one impression in 

 each valve, as the common Oyster, fig. 180 ; 2nd. The Dimy- 

 ana, those which have two, and consequently have two impressions 

 in each valve. There are other smaller impressions in some shells 

 besides the principal. The palleal impression is a mark or scar 

 passing near the margin of the shell. See Introduction. 



MY A. Auct. Fam. Myaria, Lam. Pyloridea, Bl. — Descr. Trans- 

 verse, oval, thick, gaping at both extremities, rounded anteriorly, 

 acuminated posteriorly; hinge with one large, dilate, compressed 

 tooth in one valve, and a suture in the other, containing the 

 cartilage ; muscular impressions two, distant, large, irregular ; 

 palleal impression with a large sinus. — Obs. Mya may be known 

 by the large, prominent, broad tooth in one valve In Anatina 

 there is one in each valve, and, in Lyonsia, accessory pieces. 

 Lutraria has cardinal teeth and a ligamentary pit. Few species of 

 Mya are known. They belong to the Northern Hemisphere. M. 

 truncata, fig. 71. 



MYCETOPODA or MYCETOPUS. D'Orb. Fam. Nayades, Lam. 

 — Descr. Shell elongated, soleniform, inequivalve, inequilateral, 

 gaping anteriorly; muscular impressions very complex. — Obs. 

 These shells are said to terebrate like Pholas. Fig. 151. M. 

 solenoides. 



MYARIA. Lam. A family belonging to Lamarck's order Conchi- 

 fera Dimyaria. Containing the following genera: 



1. Anatina. Ligament in a spoon-shaped prominence on the 



hinge of each valve, shell thin. Fig. 69. 



2. Mya. Spoon-shaped prominence in one valve ; shell thick. 



Fig. 71. 



3. Anatinella. A spoon-shaped process in both valves. 



Fig. 70. 



4. Lyonsia. An internal bony appendage on the hinge, 



Fig. 491,492. 



5. Myochama. Flat valve attached, a bony appendage on the 



hinge. Fig. 73. 



o 2 



