28 DESCllIPTIONS OF 



and double in both valves ; lateral teeth lamellar, rather long, curved, single in the 

 right and double in the left valve, thickened towards the posterior end ; the two 

 inferior anterior cicatrices confluent, the superior one distinct ; posterior cicatrices 

 confluent ; dorsal cicatrices placed in a row across the cavity of the beaks ; cavity of 

 the shell very shallow ; cavity of the beaks very shallow and subangular ; nacre 

 white. 



Bemarrlis. — The specimen above described is probably quite a young one, and I have 

 great doubt of its really being a native of Arabia. Among many fine shells brought 

 by Captain Brown, from nearly all parts of the world where he carried on his 

 commercial affairs, were many rare and fine specimens from the rivers of South 

 America. This specimen was marked in one valve " Mocha ;" in the other, " Red 

 Sea ;" so that he most probably purchased it in Arabia ; and still it may have been 

 brought there by trading vessels from South America, having some of the characters 

 of that habitat, particularly the diverging costge on the beaks ; which character so 

 peculiarly belongs to most of the species of that quarter of the globe. It seems to 

 be more nearly allied to JJ. Paranensis, (nobis,) than to any species I am acquainted 

 with, but it is not so rotund, nor is it so much inflated along the umbonial slope. The 

 costa of the beaks are smaller, and the epidermis is green and not brown as in 

 Paranensis. It is also somewhat like U. Burroughianus, (nobis,) from South 

 America, but is not so transverse as that species, and is not so high on the umbonial 

 slope. On the posterior slope there are two distinct rays from the beak to the margin, 

 one being yellow and the other dark green. I name this in honor of the late Captain 

 Brown, of Beverly, Mass.. to whose kindness I owe the possession of the specimen. 



Unio Wheatleyanus. PL 29, fig. 23. 



Testa Isevi, elliptica, inflata, inasquilaterali; valvulis crassis; natibusprominulis, costis elevatis ; epidermide 



tenebroso-oliva, rugoso-striata ; dentibus cardinalibus nia^nis, crassiusculis, subdivisis j lateralibus 



loDgis crassisque ; margarita vel alba vel carnea et iridescente. 



Shell smooth, elliptical, inflated, inequilateral ; valves thick ; beaks a little 



prominent with large ribs ; epidermis dark olive and rugosely striate ; cardinal teeth 



large and somewhat thick, subdivided ; lateral teeth long and thick ; nacre white or 



flesh colored and iridescent. 



Proo. Acad. Nat. Sci. Vol. 8, p. 94. 

 Hab.— Rio Plata, Mr. D'Orbigny ; Rio Negro, Mr. Wheatley. 



My cabinet and cabinet of Mr. Wheatley, New York. 

 Diam. 1-2,- Length 1-9, Breadth 2-8 inches. 



Shell smooth, elliptical, inflated, inequilateral, elevated on the posterior slope; 

 substance of the shell thick, thinner behind ; beaks a little prominent, with divergent 

 and re-entering ribs at the apex ; ligament rather short and stout ; epidermis dark 

 olive, rugosely striate and apparently without rays ; umbonial slope obtusely angular ; 



