unio. 147 



— Kickx, Moll. Brabant. Austral, p. 82. — Rossmasl. 



Iconog. Land and Siissw. Moll. pt. 1, p. 120, pi. 4, f. 71, 



72, 73, 74 ; pt. 2, pi. 8, f. 129. — Hanl. Recent Shells, 



vol. i. p. 213. 



Unio elo>?gala, Lam. Anim. s. Vert, (ed Desh.) vol. vi. p. 531.— Nilsson, Moll. 



Sueciee Terr, et Fluv. p. 106. — Michaud, Comp. Moll. Terr, et 



Fluv. France, p. 113, pi. 10, f. 29.— Gras, Moll. Terr, et Fluv. 



France, Append, p. 22. 



Alasmodonta arcuata, Barnes, Silliman's Journal, vol. vi. p. 277, pi. 12, f. 20. — 



Gould, Invert. Massach. p. 113, f. 75 (Alasmodon). 

 Unio sinuate, Pkeif. Deutsch. Land und Siissw. Moll. pt. 2, p. 33, pi. 7, f. 4. 

 „ Boissi/i, Michaud, Comp. Moll. Terr, et Fluv. France, pi. 16, f. 28 (fide 

 Rossm.) 

 Alasmodon margaritiferus, Fleming, Brit. Anim. p. 417. — Gray, Manual Land 

 and F. W. Shells, p. 293, pi. 2, f. 9. — Thompson, 

 Ann. Nat. Hist. vol. vi. p. 197. — Macgilliv. Moll. 

 Aberd. p. 242. — Brown, 111. Conch. G. B. p. 83, 

 pi. 30*, f. 1, 2, 3, 4 ; pi. 31, f. 1, 2 ; pi. 32, f. 13, 

 14, 15. 

 Mai-garitananiargaritifera, Lea, Trans. Americ. Phil. Soc. vol. vi. p. 135. 



The arcuated shape, and consequent incurvation of the ven- 

 tral margin, in most examples of this well-known bivalve, 

 has induced the separation of the straighter individuals as 

 a distinct species. Believing- as we do, that the Naiades 

 have been most unnecessarily subdivided and multiplied, 

 we have felt disposed to include likewise the U. sinuatus of 

 Lamarck, but have been deterred, by the high authority 

 of Rossmiisler and Deshayes, from thus extending our 

 synonymy. 



The ordinary form is oval-oblong, or elongated kidney- 

 shaped ; the valves are thick and strong, compressed when 

 young, moderately ventricose when adult, covered with a 

 strong epidermis of an uniform pitchy black (which is of a 

 lighter or yellow cast in the immature specimens) smoothly 

 spread upon the disk, but more loosely disposed towards 

 the margin and posteriorly; occasionally the surface is 

 obsoletely waved with very obscure concentric plica?. The 

 ventral margin is cither incurved, straight, or at most very 



