ALASMODON. 277 



128. 1. ALASMODON margaritiferus. Pearly Alasmo- 



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. 149/; Schroet Flmsc. 168. t. 4. f. 1. Unio 

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

 n. 1. ; 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. 1719. ; 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. 1 12. t. 16. f. 28. ; 

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

 Roissyi. Forbes, Malac. Man. 44. Alasmodon margariti- 

 ferum. Fleming, B. A. 417. Damaris elongata. Leach, 

 Syn. Moll. 322. Margaritana fluviatilis. Schum. N. Syst. 

 124. Alasmodon margaritiferus. Gray, Man. 293. 

 Margaritana margaritiferus. Dupuy, Cat. n. 213. U. mar- 

 garitana margaritifer, and Lymneus sinuatus. Moq. Tand. 

 Moll Franc, ii. 266, 267. Unio rugosa. Poir. Prod. 205. 

 Unio crassissima, Feruss.; Des Moul. Moll. Girond. 42. 

 Unio sinuatus. Ross. Icon. n. 3. Unio brunnea. Ponti, 

 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 



