24 NEW UNIONID^ OF THE 



brown, darker before and behind, with somewhat close marks ot growth ; umbonial 

 slope rather low and subbiangular; posterior slope somewhat raised, with two 

 iridescent impressed lines on each from the beaks to the margin; cardinal teeth 

 rather large, crenulate, striate, nearly perpendicular and disposed to be double in the 

 right as it is in the left valve ; lateral teeth very long, nearly straight, finely 

 granulate and enlarged toward the end ; anterior cicatrices large, well impressed and 

 distinct ; posterior cicatrices large and confluent ; dorsal cicatrices placed above in the 

 centre of the cavity of the beaks ; cavity of the shell very shallow and very wide ; 

 cavity of the beaks very shallow and rounded ; nacre purple or salmon color and 

 very iridescent. 



Soft parts. — BmncJiial uterus not charged, but well developed ova were found in 

 the ovarium. BrancJiias very large, thin, inner ones larger before, free nearly the 

 whole length of the abdominal sack. Paljpi small, nearly transverse, suboval, attached 

 nearly the whole length of the posterior edges. Mantle thin, slightly colored on the 

 lower edge. Branchial opening rather large, with numerous small brownish papillsB 

 on the inner edges. Anal opening large, with numerous small dark brown papillte 

 on the inner edges. Super-anal opening long, colored within and united below. Color 

 of the mass whitish. 



Remarks. — There were five specimens received from Mr. Pratt, in alcohol, but none 

 had ova in the branchial uterus, which, therefore, cannot be described. This species 

 belongs to the complanatus group. In outline it is near to Boanohensis (nobis) and 

 Ne%isensis (nobis). It is by no means so large a species as the former, nor so thick ; 

 but it is larger than the latter. It has the broad truncate posterior margin as they both 

 have. It is most closely allied to Neusensis, but may be distinguished by its not being 

 so high on the umbonial slope, and not being so much compressed down the middle of 

 the disk. The Neusensis is also a more solid shell, and the nacre is usually of a strong 

 deep purple, while Roswellensis is more disposed to be salmon color. In the mature 

 individuals there are no rays visible, but in a young specimen obscure rays are 

 observable on the sides. 



Unio Prattii. pi. 24, lig. 88 and 8Sa. 



Tfsta laevi, ulliptica, siibiiiflata, pustice obliqui: ct autici! regularitcr rotunJata, iiicquilatuiali; valvulis 

 subtenuibus, anticd crassioribus; natibus subprominentibus, crass6 undulatis ; epidermidc tcnebrosa, 

 valde radiata; dcntibus oardinalibus parviusculi.s, crenulatis, obliquis, in utroquc valvulo diiplicibus ; 

 lateralibus sublongis subrectisque ; margarita alba et valde iridescente. 



Shell smooth, elliptical, rather inflated, obliquely rounded behind and rounded 

 before, inequilateral ; valves rather thin, thicker before ; beaks somewhat prominent, 

 thickly undulate; epidermis very dark, very much radiated; cardinal teeth rather 

 small, crenulate, oblique and double in both valves ; lateral teeth rather long and 

 nearly straight ; nacre white and very iiidesoent. 



Proc -\c-:.d. Nat, S,-i., Is.",*, ,,. ICil. 



