t>4 MYA. 



hinge with two teeth diverging- at the apex, 

 and inserted into corresponding linear cavi- 

 ties. 



Mya variabilis. Maton in Lin. Trans, x. p. 327. t. 24. f. 4 

 to 7. Wood's Conch, p. ] 1 J. 



Inhabits rivers in South America. Maton. 



Shell about an inch long, and rather less in breadth, striated 

 transversely, and longitudinally wrinkled at the beaks ; it is 

 coated with a brown epidermis, and the inside is pearly, with 

 a bluish tinge; the margin at the anterior end is somewhat 

 angular, and forms a strait line at the hinge ; young shells are 

 of a purple colour within, and have the prominent wrinkles 

 diverging from the apex nearly to the margin. Dr. Maton 

 says this species varies extremely in its structure and contour, 

 according to its several stages of growth, so that if he had not 

 had opportunities of comparing those of intermediate ages 

 together, he should most probably have given them separate 

 places in the genus. When a similar opportunity occurs for 

 examining M. corrugata and M. rugosa, it will probably be 

 found that they also owe their difference of form solely to 

 difference of age. 



nodosa. 33. Shell oval, thin, with raised tubercles 

 about the beaks. 



Mya nodosa. Chemnitz, x. p. 347. t. 170. f. 1650. Gme- 

 lin, p. 3222. Wood's Conch, p. 1 10. 



Inhabits fresh waters. Chemnitz. 



Shell near three-quarters of an inch long, and about twice as 

 broad, of a greenish colour ; and smooth, except about the 

 beaks, which are surrounded by a few knotty protuberances. 



syrmatophora. 34. Shell ovate, depressed ; hinge 

 with an awl-shaped projection on the margin 

 of the primary tooth, and that of the other 

 valve dilated. 



Mya syrmatophora. Gronovius Zooph. p. 260. t. 18. f. 1 

 and 2. Schroeter Einl. ii. p. 62O. Gmelin, p. 3222. 

 Wood's Conch, p. 1 10. 

 Inhabits rivers in Guinea. Gronovius. 



Shell about two inches and a quarter long, and two inches 

 broad, and in its shape bears some resemblance to a young 

 shell of Mytilus margaritiferus, but the hinge is totally dif- 

 ferent. 



