278 Dr. Hildreth on fresh water Shells. 



I have as yet noticed but one variety of Univalve, in our 

 streams ; neither have I been able to collect all the species 

 of the bivalve, as I have heard of several, which are not in 

 my collection. — The description of most of my shells is taken 

 from the observations of Mr. Barnes, published in the 6th 

 vol. of the Journal of Science ; a gentleman who deserves 

 much credit for his devotedness to American natural history. 



Remarks. — My collection is generally made up of living 

 subjects ; and the color, &c. for the drawings, selected from 

 several individuals of the same species. — The drawings were 

 executed by Mr. Sala Bosworth, a young self taught artist 

 of Marietta. 



Genus Unio. 



Generic character, from M. Lamarck. 



" Shell transverse, equivalve, inequilateral, free, beaks de- 

 corticated, somewhat carious ; posterior muscular impression 

 compound ; hinge with two teeth in each valve ; the cardin- 

 al one short, irregular simple, or divided into two, substriated ; 

 the other elongated, compressed, lateral, extending beneath 

 the corslet. Ligament exterior." 



Remarks. — Not expecting by these observations to throw 

 much light on the study of Conchology, but only to des- 

 cribe the shells in this vicinity, I shall not divide the genus 

 into classes, or parts, but go on as they are numbered in the 

 drawings — the measure is by inches and decimals. 



, T , TT r, -p ■ * ) A. outside of the 



No. I. Unio CEASsus.-Fig. I. J sheUi C . inside . 



Shell very thick, tumid ; cardinal teeth lobed, angulated ; 

 posterior cicatrix deep and rough. — Hab. Muskingum. 



Length, 3 inches ; breadth, 4 inches ; diameter 2 do. 



Shell very thick, and oval — rounded behind, slightly an- 

 gulated before ; epidermis light brown ; surface waved ; 

 beaks projecting ; cardinal teeth deeply sulcated ; anterior- 

 cicatrix striated ; cavity of the beaks capacious, but not 

 deep ; naker, (or inside of the shell) pearly white and 

 iridescent. 



Remark. — It is a very common shell, and abounds in va- 

 rieties. 



No. 2. Unio Ellipticus. — Fig. 2. 



Shell regularly oval ; thick, convex, glabrous, beaks de- 

 pressed ■ teeth elevated, triangular, striated.-^Hab. Musk- 

 ingum. 



