— 12 — 
Weichkörper unbekannt, 
Nur die eine Art M. laosensis Lea. 
Margaritänopsis laosensis Lea. 
Taf. 12, Fig. 1—2. 
Unio laosensis Lea, Proc. Ae. Nat. Sciences, Philadelphia, VII, 1863, p. 190. — Journal 
Ac. Nat. Scienees, Philadelphis, VI, 1866, p. 63, Taf. 21, fig. 61. — Ob- 
servations ges. Unio, XI, 1867, ». 67, T. 21, fig. 61. — Sowerby, Conch. 
Ican., XVI, 1866. T. 47, fig. 256, — Paetel, Catal. Conch. Samml,, IIT, 
1890, p. 156. 
Margaron (Unio) laosensis Lea, Syn., 1870, p. 62. 
Unio suls Theobald, fide Simpson, Syn.. 1900, p. 678. 
Unio sella Tapparons-Canefri, in manuscriptis. 
Margaritana laosensis Simpson, Syn. 1900, p. 678. 
Testa laevi, arcuata, in medio compressa, valde inaequilaterali, antice et postice rotun- 
dato; valvulis suberassis; matibus prominulis, subcompressis; epidermide tenebroso-fusca vel 
rufo-fusca, postice obsolete radiata,; dentibus cardinalibus parvis, striatis, lobatis; lateralibus 
zongis, corrugatis subrectisgue, margarita alba et üridescente. 
Shell smooth, arcuate, compressed in the middle, very inequilateral, rounded before 
and behind, disposed to be sulcate before; substance of the sheli semewhat thick, beaks a 
liitie prominent and somwhat compressed; ligament long and light brown; epidermis dark 
brown or reddish brown, obscurely rayed bekind and with distant marks of growth; umbonial 
slope slightly raised and rounded; posterior slope long and narrew, slightly carinate, and 
with a single dark ray from the beaks to the posterior margin on each valve; cardinal teeth 
small, striate and somewhat lobed; lateral teeth long, somewhat rough and nearly straight; 
anterior cicatrices distinct, rather large and well impressed; posterior cicatrices distinct, 
large and slightiy impressed; dorsal cicatrices placed above the centre of the cavity of the 
beaks; ventral eicatrices small and dotted over the middle of the disk; cavity of the thell 
wide and shallow; cavity of the beaks rather shaliow and obiusely angular; nacre white and 
iridescent. 
Hab. — Laos Mountains, Cambodia, Siam, Mons. Mouhot, per. H. Cuming, Esqu. 
Diam. 0,9, Length 1,2, Breadth 3 inches. 
Lea. 
Schale länglich nierenförmig, vorn und hinten ‚gerundet, vorn klaffend, ziemlich fest bis 
fest. Vorderer Oberrand gerade oder leicht gebogen abfallend, ohne Eckein den Vorderrand 
übergehend. Unterrand in der Mitte stark eingedrückt, ohne deutliche Ecke in den Hinter- 
