jy DESCRIPTIONS OF 



falls much shorter than the lower section. The beaks of both specimens are eroded, 

 but there are marks observable along the anterior slope, which display a single row 

 of an unusual form, but too indistinct to describe clearly. 



Unio Myersianus. pi. 22, fig. 2. 



Testil bialata, lEevi, triangulari, subcompressa, inasquilaterali, postic^ angulata; valvulis crassis; natibus 

 prominulis ; epidermide tenebroso-fusca ; dentibus cardinalibus longis erenulatisque ; lateralibus proe- 

 longis, lamellatis subcurvisque ; margarita colore salmonis tincta. 



Shell with two wings, smooth, triangular, rather compressed, inequilateral, angular 

 behind ; valves thick ; beaks somewhat prominent ; epidermis dark brown ; cardinal 

 teeth long and crenulate ; lateral teeth very long, lamellar and somewhat curved ; 

 nacre salmon colored. 



Proc. Acad. Nat. Sci. Vol. 8, p. 92. 



Hab.—Siam. S. R. House, M. D. 



My cabinet, cabinets of W. A. Haines, New York, and Dr. Ingalls, Greenwich, N. Y. 

 Diam. 1-6, Length 3-6, Breadth 5-G inches. 



Shell with two wings, connate before and behind, smooth, triangular, rather com- 

 pressed, inequilateral, angular behind and rounded before ; substance of the shell 

 thick ; beaks a little prominent ; ligament long, large and concealed ; epidermis dark 

 brown, with two obscure lines passing from the beak to the posterior basal margin ; 

 umbonial slope obtusely angular ; marks of growth distant and indistinct ; cardinal 

 teeth disposed to be double in both valves, but more so in the right, crenulate : lateral 

 teeth very long, lamellar, somewhat curved and joined to the cardinal tooth : anterior 

 cicatrices all three very distinct ; posterior cicatrices very indistinctly marked, con- 

 fluent ; dorsal cicatrices deeply marked in the centre of the cavity of the beak ; pal- 

 leal cicatrix deeply impressed ; cavity of the shell somewhat deep : cavity of the beaks 

 rather shallow and subangular ; nacre salmon colored and iridescent. 



BemarJcs. — There is a very close resemblance between this and Housd, herein 

 described, and they may possibly prove to be merely strong varieties when complete 

 suites are obtained. There are some sixteen specimens of the two before me, and they 

 can be separated by the crenulated cardinal teeth of Myersianus, which species is also 

 larger and more ponderous. The oldest specimens have the teeth flatter and more 

 crenulate. In some of the specimens the cicatrix of the superior anterior tractor 

 muscle is separate from the other anterior cicatrix, and deeply impressed. Unfor- 

 tunately not one of the specimens has a perfect wing before or behind, but there re- 

 mains evidence of their being somewhat elevated. This is one of the fine shells 

 procured by Mr. Haines from Bangkok, through the kindness of Mr. John K. Myers, 

 of New York, after whom I name it. 



