ALASMODON. 
277 
128. 1. Alasmodoist 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. Lmn. Fauna Suec. 516., Syst. Nat. ii., 
List. Conch. 149.^; Schroet. Flussc. 168. t. 4, f. 1.— Unio 
margaritiferus. Itetz. 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. Bray. 132. t. 10. f. 17—19. ; Pfeiffer., i. 116. t. 5. 
£ 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 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 
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