52 MY A. 



Shell rather more than two inches long, and about three and a 

 half broad ; the substance is thick, the beaks decorticated, 

 and the inside of a rose colour. Gmelin, with a mark of 

 doubt, has cited Lister's figure for a variety of Mylilus cyg- 

 neus, but it has obviously the hinge of a Mya. 



nodulosa. 28. Shell sub-oval, and studded with 

 tubercles ; hinge with a thick crenated tooth. 

 Mya nodulosa. Wood's Conch, p. 106. t. 22. f. 1 to 4. 



Inhabits 



This Shell varies in shape from roundish to oval, and in diame- 

 ter from one inch and a quarter to twice that size ; it may 

 be readily known by the outer surface of its remarkably thick 

 valves being studded all over with broadish tubercles. The 

 teeth are said by Mr. Wood, who alone has described this 

 species, to be thick and clumsy like those of M. ponderosa. 



margaritifera. 29. Shell ovate, compressed on 

 the fore part ; primary tooth of the hinge co- 

 nical, and the beaks decorticated. 



Mya margaritifera. hinnaus Syst. Nat. p. 1112. Midler 



Verm. p. 210. Pennant Zool. iv. p. 80. t. 43. f. 18. 



Schroeter Fluss. p. 168. t. 4. f. 1. Born. Mm. p. 21. 



Chemnitz, vi. p. 15. t. 1. f. 5. Schroeter Finl.u. p. 606. 



Da Costa Brit. Conch, p. 225. t. 15. f. 3. Gmelin, 



p. 3219. Barbnt. p. 18. t. 2. f. 2. Schrebers Conch. 



ii. p. 3. Donovan, iii. t. 73. Montagu Test. p. 33. 



Maton and Racket in Lin. Trans, viii. p. 40. 

 Unio. Erie. Method, t. 240. f. 5. 

 Lister Anim. Ang. t. 1. f. I. Conch. 1. 149. f. 4. Klein. 



Ost. t. 10. f. 47. Knurr, iv. t. 25. f. 2. Favanne, t. 62. 



f.F. 

 Inhabits rapid rivers, and mountainous torrents, in most parts 



of the north of Europe. Britain. Lister, fyc. 

 Shell sometimes two and a half inches long, and near six inches 

 broad; strong, ponderous, and coated with a thick black epi- 

 dermis; the shape is rather more oblong than ovate, and the 

 margin opposite the hinge is arcuated ; hinge strong, consist- 

 ing of a single tooth in one valve, which locks into a bifur- 

 dcate one on the other ; the inside is pearly, and sometimes 

 produces pearls of a considerable size. 



corrugata. 30. Shell rhombic, green, and wrin- 

 kled at the beaks. 

 Mya corrugata. Mailer Verm. ii. p. 214. Schroeter Fluss. 



