36 DESCRIPTIONS OF 



that of Unk) crjUndricus, Say, but it is a much thinner shell and entirely without 

 tubercles, which are so remarkable on the umbonial slope of that species. It is closely 

 allied to U. Popeii, (nobis,) but is not so much compressed, is diflFerent in color, more 

 cyclindrical as well being furnished with granules. The epidermis of Poeyanus is very 

 remarkable. It is very thin and firmly attached to the calcareous matter, and 

 when examined with a good lens very minute granules may be seen over the surface ; 

 at the anterior part the striae are imbricate. The two specimens differ in color. 

 The younger, being half grown, is of a straw yellow, while the older one is an olive 

 yellow to that point of growth, and straw yellow beyond that to the margin. The 

 younger is entirely without rays, while the older has obsolete rays on the posterior 

 portion. 



Anodonta Holtonis. pi. 32, fig 31. 



Testa IjBvi, oblonga, inflata, valde inasquilaterali, e natibus lineatis ; valvulis subcrassis; natibus subprominen- 

 tibus ; epidermide tenebroso-olivacea, striata ; margarita caBrulea et valde iridescente. 



Shell smooth, oblong inflated, very inequilateral, with diverging lines from the beaks ; 

 valves rather thick ; beaks somewhat prominent ; epidermis dark olive, striate ; nacre 

 bluish white and very iridescent. 



Proe. Acad. Nat. Sci. 1857, p. 85. 



ffab. — Near Cartago, New Granada. Rev. J. F. Helton. 

 My cabinet and cabinets of Mr. Holton, Mr. Wheatley and Lyceum of Nat. Hist., 



New York. 

 Diam. -9, Length 1"3, Breadth 2-7 inches. 



Shell smooth, oblong, inflated, very inequilateral, with crimpled lines radiating from 

 the beaks, obtusely angular behind ; substance of the shell rather thick ; beaks somewhat 

 prominent ; ligament rather long and thin ; epidermis dark olive, minutely crimpled 

 over the posterior slope and crimpled in lines on the sides from the beaks to the basal 

 margin, with three obscure greenish lines on the posterior slope ; umbonial slope slightly 

 rounded ; marks of growth distant and not very distinct : anterior cicatrices distinct, 

 the adductor being very large, the tractor very small : posterior cicatrices large and 

 confluent ; dorsal cicatrices small and placed on the upper side of the cavity of the 

 beaks ; 'pallial cicatrix slightly impressed ; cavity of the shell deep and rounded ; 

 cavity of the beaks rather deep and subangular ; nacre bluish white and very iridescent. 

 Remarhs. — This species, of which I have but a single specimen before me, was 

 brought by the Rev. Mr. Holton from the upper Cauca, interior of New Granada, 

 where they are found in abundance, in " a pond, like the Illinois Prairie Ponds, an 

 acre in extent, with muddy shores, being G to 15 feet deep in the centre, without inlet 

 or outlet, and not surrounded by marshy ground, the distance from the Cauca River 

 being 5 miles. This pond is within half a mile of Cartago." 



