A0 _. Dr. Marow's and Mr. RAckETT's 
distinct species, as their dissimilarity in shape cannot 
* therefore be imputed to a difference in place of abode. 
They are also found in the rivers Froome and Avon, 
Somersetshire, and the New River, near London. 
Li. p lo eS pep SE EMI SEI S 
margari- M. testa ovata antice coarctata, cardinis dente prima- ‘ 
tifera. rio conico; umbonibus decorticatis. Linn. Fauna 
Suecica, 2130. ye. Nat. p 1112. n. 29. Linn. Gmel. 
p. 3219. 
Lister Anim. Angl. App. t: T... 
Conch. t. 149. f. 4. 
Knorr. Vergn. À. t. 25. f. 2. 
Schrot. Flussconch. t. 4. f. 1. — 
Pennant Brit. Zool. 4. t. 43. f. 18. 
„Da Costa Brit. Conch. p. 225. t. 15. fad 
— Donovan Brit. Shells, t. 13. 
Montagu Test. Brit. p. 33, 
Halitat in fluviis. | 
Testa ovali-oblonga, ponderosa, antice retuso-compressa, extus rudis nigri- 
cans, 2 vel 2; pollices longa ad 54 lata, umbonibus valde decorticatis, 
Intus testa albida, matricem perlarum exhibens cicatricibus duabus 
pro insertione musculorum, valvulis clausis nec hiantibus, ` 
Cardinis dens conicus obtusus porrectus in alterius m dentem latum 
fissum. (Linn. Fn. Suec.) ; 
First described and figured by tiie Found in 
rapid rivers and rocky torrents in the North, in Wales, 
wdi in Devonshire. 
E eme Da N 
inequival-M. testa subtriangulari ; me T incurvatis gibbis. 
vis. Walker Test. Min. Rar. t. 3. f. 85. der x 
t. 1. f.6. Encyclop. Method. (230. Fha 
Montagu Test. Brit. p.38. 
. Habitat in mari, 
Testa 
