280 Dr. Hildreth on fresh water Shells. 



wrinkled transversely ; oblique folds, deeply indenting the 

 anterior margin, furrows largest and deepest on the center 

 of the disks and extending to the anterior basal margin, de- 

 cussating the oblique waves ; large oblong tubers below the 

 beaks ; cardinal teeth sulcated and crenated ; posterior ci- 

 catrix very rough and shallow ; naker pearly, irregularly 

 spotted with olive, and most beautifully iridescent from the 

 termination of the ligament to the anterior basal margin, af- 

 fording the richest display of colors, in which violet and 

 purple predominate, of any shell in my collection. 



No. 5. Unio Plicatus. — Fig. 5. 



Shell sub-quadrangular, tumid with distant oblique folds ; 

 hinge margin elevated, compressed, carinated. — Hab. Musk- 

 ingum. 



Length, 2.8 ; breadth, 2.9 ; diameter, 17. 



Shell thick, posterior side short, obtusely rounded ; ante- 

 rior side compressed wedge shaped ; beaks very prominent 

 and projecting backwards as far as the posterior side ; lig- 

 ament elevated and passing between the beaks ; hinge mar- 

 gin higher than the beaks ; epidermis greenish ; surface 

 glabrous, deeply folded, indenting the anterior basal edge ; 

 cardinal teeth, sulcate, crenate ; lateral in the left valve, cur- 

 ved, and extending up back of the cardinal tooth ; poste- 

 rior cicatrix rough and deep ; cavity of the beaks deep and 

 extended backwards ; naker white, iridescent on the fore 

 part, and tinged with gold color on the corslet and anterior 

 edge. 



Remarks. — This shell does not correspond, in all partic- 

 ulars, with Mr. Barnes's Plicatus, but still I think it the same. 

 It will stand erect very firmly when placed on the posterior 

 side.* 



No. 6 & 7. Unio Undatus. — Figs. 6 and 7, two varieties. 



Shell sub-orbicular, very tumid ; waved ; lateral teeth, two 

 in each valve. White variety, length, 2.25 ; breadth, 2.5 ; 

 diameter, 1.5— Hab. ]\tuskingum. 



Shell thick, disjks swelled behind, depressed before ; beaks 

 projecting backwards nearly as far as the posterior side, 

 elevated and recurved, with the ligament passing between 

 them ; anterior lunule long heart shaped ; disks waved trans- 



* Mr. Barnesj we are informed, considers it »s a variety of the following.— Ed. 



