APPENDTX. 883 



curved, compressed, extremely inequilateral, rather thick (not solid), 

 obliquely and very bluntly subbiangulated in front, narrowly rounded 

 behind, of an uniform brownish black, adorned with numerous sub- 

 angular isolated tubercular divergent undulations upon, and in front 

 of, the broad and rounded (yet not elevated) umbonal ridge, beyond 

 which the surface is abruptly flattened, closely and coarsely grained 

 (or finely tuberculated), and then merely wrinkled by the lines of 

 growth ; ventral edge retuse behind the middle ; umbones not at all 

 prominent: inside silvery ; cardinal teeth small, yet strong. 2... 5. 

 Australia. 



Unco Hembeli (t. 24, f. 3), Conrad, Mon. U. p. 93, t.51. Oblong- 

 elliptical, very inequilateral, rounded behind, bluntly subcuneiform 

 (when adult) in front, moderately strong, compressed, of an uniform 

 pitch-brown, concentrically wrinkled, and studded with somewhat 

 divergently disposed tubercular elevations on the ordinary site of the 

 umbonal ridge ; ventral edge retuse in the middle ; ligamental edge 

 convex ; umbones eroded, scarcely projecting above the dorsal line ; 

 ligament long, tawny ; inside white ; cardinal teeth solid ; lateral 

 crenulated. 1^...3i. Louisiana. 



A. b. **** Non-symjihonote s?nooth or concentrically sulcated 



Uniones proper. 



Unio Siculus (t. 20, f. 19), Swainson, Malac.p. 282,/. 58. Pro- 

 duced-oblong, very inequilateral, thick, subventricose, yellowish olive 

 arranged in lighter and darker concentric shades, not rayed, smooth 

 (except the lines of growth) ; ventral edge retuse in the middle, rising 

 in an oblique curve posteriorly : anterior extremity very bluntly sub- 

 cuneiform, ligamental edge subparallel with the ventral ; hinder side 

 occupying two-sevenths only of the total measurement, its extremity 

 subangulated dorsally, rounded ventrally ; no conspicuous umbonal 

 ridge ; umbones little raised, the corrugations indistinct ; nacre white, 

 umbonal cavity tolerably arnple ; the inner cardinal teeth large, solid, 

 jagged. 1^...3^. Sicily. The specimen described came from Lake 

 Leontini, and was, I believe, one of Swainson 's. Lea, perchance 

 correctly, refers the species to U. pictorum. 



Unio subplanus (t. 21, f. 16), Conr. Mon. U. t. 41, /. 1. Semi- 

 rhombic - oval, moderately inequilateral, subbiangulated in front, 

 rounded behind, thickish, subcompressed, pitch-brown, not rayed, 

 smoothish ; umbonal ridge inconspicuous ; ventral edge arcuated 

 behind, subparallel in front to the scarcely convex anterior dorsal 

 edge ; umbones eroded, not prominent ; cardinal teeth strong, tri- 

 angular; lateral teeth elongated. \\...%. Virginia. 



