ALASMODON. 277 



128. 1. Alasmodon margaritiferus. Pearly Alasnio- 



don. — Shell ovate-elongate, rather compressed, 



thick, heavy, black-brown, truncated below; 



cardinal teeth thick, conical, (t. 2. f. 9.) 



Young with small posterior lateral teeth, like 



Unio. 



Unio riparia. Pfeiffer, t. 5. f. 13.?? — Unio margaritifera. 

 Pfeiffer, ii. t. 7. f. 1. 



Mya margaritifera. Linn. Fauna Suec. 516., Syst. Nat. ii., 

 'List. Conch. Ug.'; Schroet. Flussc. 168. t. 4. f. 1.— Unio 

 marffaritiferus. Retz. Nov. Gen. 16. 1788. ; Nilson, 103. 

 n. L'; Turton, Biv. 242. t. 16. f. 1., Man. ed. 1. 19. f. 9. ; 

 Forbes and Hanley, B. M. ii. 146. t. 38. — Unio margariti- 

 fera. Drap. 132. t. 10. f 17—19.; Pfeiffer, i. 116. t. 5. 

 f. 11. — Unio sinuata. Lam. H. vi. 70.; Pfeiffer, ii. 33. 

 t. 7. f. 4. — Unio margaritifer. Rossm. Icon. i. 122. f. 72. 

 74., ii. 21. f. 129. — Unio elongatus. Nilson, 106. n. 2. — 

 Unio elongata. Lam. Hist. vi. 70.; Mich. Compl. 113. 

 t. 16. f. 29.— Unio Roissyi. Mich. Compl. 112. t. 16. f. 28.; 

 Proceed. Brit. Assoc, for 1838. — Unio margaritifera, forma 

 Roissyi. Forbes, Malac. Mon. 44. — Alasmodon margarlti- 

 ferum. Fleming, B. J.. 417. — Damaris elongata. Leach, 

 Syn. Moll. 322. — Margaritana fiuviatilis. Schum. N. Syst. 

 124. — Alasmodon margaritiferus. Gray, Man. 293. — 

 Margaritana margaritiferus. Ditpuy, Cat. n. 213. — U. mar- 

 garitana margaritifer, and Lymneus sinuatus. Moq. Tand. 

 Moll. Franc.\\. 266, 267. — Unio rugosa. Pair. Prod. 205. 

 — Unio crassissima. Feruxs.; Des Maul. Moll. Girond. 42. — 

 Unio sinuatus. Ross. Icon, n, 3. — Unio brunnea. Poiiti, 

 Bivalve Rodez, 430. 



Inhab. mountain rivers with a rocky bed. 



M. Moquin Tandon divides these species between 

 two sub-genera, one, Margaritana margaritifer, and 

 the other, Lymneus sinuatus, the latter being the 

 adult shell. 



The young specimens are oblong, without any con- 

 traction in the lower edge ; and in some rivers the 

 shell appears to retain this appearance in its adult 



T 3 



