CHIEFLY OF THE UNFrEU STATES. 29 



G. W. Tryon, Jr.; Flemingtou, Conn., Prof. Shepard ; Westfield, Mass., Dr. Shurt- 

 leff; and Potomac, near Chain Bridge, above Washington, Prof. Henry. 



My cabinet and cabinets of Mr. Tryon, Academy of Natural Sciences and Smith- 

 sonian Institution. 

 Diam. ], Length 1-7, Breadth 28 inches. 



Shell smooth, obliquely elliptical, rather compressed, sublenticular, very inequi- 

 lateral, subbiangular behind, rounded before ; substance of the shell thin ; beaks a 

 little prominent, somewhat compressed, undulate at the tips with double curves ; 

 ligament rather long, somewhat thin and light brown ; epidermis shining, green or 

 dull brown, ob.scurelv radiate, with distant and usually with broad dark brown lines ' 

 of growth ; umbonial slope slightly raised and rounded ; posterior slope narrow 

 elliptical, very slightly raised, with three dark rays from the beaks to the margin on 

 each valve; anterior cicatrices confluent, large and very slightly impressed; posterior 

 .cicatrices confluent, large and slightly impressed; dorsal cicatrices very small and 

 placed nearly in the centre of the cavity of the beaks; cavity of the disk rather 

 shallow and very wide ; cavity of the beaks very shallow, scarcely observable ; 

 nacre bluish white and iridescent. 



Remarlis. — Many years since I observed, though of very rare occurrence, a com- 

 pressed Anodonta, which I considered then a variety of the conimon Jiaviaiilis. Sub- 

 sequently 1 received specimens of the same character from Prof. Shepard, from 

 Connecticut, and Dr. ShurtleiF, of Massachusetts. Very recently Mr. Tryon called 

 my attention to a well characterized specimen which he found on League Island, a few 

 miles below our city. Still more recently some twenty specimens came in a box sent 

 for examination from the Smithsonian Institution. These last were of different ages 

 and stages of growth, and satisfied me entirely that the species was distinct from 

 fluviatilis, which is more transverse and more inflated. It cannot be confounded 

 with implicata, Say, which is a larger species, more transverse, and has a thickened 

 mai-gin which this has not. iNor can it be confounded with Wlllkimsu, herein 

 described, which is a larger species, more medial and has a thickened border. Some 

 of the specimens are of a dull olive brown to the first mark of growth, which is 

 broad and dark, and below which the disk is often of a fine green color. The dark 

 mark of growth is usually accompanied, on the inside, with a milk white transverse 

 band. I have great pleasure in dedicating this species to Mr. G. W. Tryon, Jr., who 

 kindly gave me his fine specimen. 



Anodonta Dallasiaka. PI. 11, fig. 28. 



Testa la3vi, subelliptioa, subinflata. iaaequilaterali, po.stice obtuse augulata, antiee rotundata ; valvulis 

 tenuibus, subdiaphanis ; natibus subelevatis, ad apices graaulatis; epidenuide luteo-viiidi vel 

 teuebrosa, ei'adiata; margarita CcEruleo-alba et iridesceute. 



Shell suiooth, subeilliptical, somewhat inflated, inequilateral, obtusely biaugular 



s 



