Mr. Barnes on the Genera Unio and Alasmodonta. 119 



with a deep cavity beneath. In others, the beaks are flat, 

 shghtly elevated, having only a small cavity within. 



Varieties. 



(a.) Oval. Mr. Say's book, pi. 1. fig. 8. 



(6.) Ovate. Mr. S. B. Collins''s collection, hab. Ohio. 



(c.) Triangular, do. do. do. 



(d.) Quadrangular. My collection. 



(e.) Orbicular. Mr. Collinses collection. 



(/.) Undulate. do. do. 



Ig.) Rugose. do. do. 



(h.) Radiate. Mr. Say^s collection Philadelphia, Ouis- 

 consin. 



(i.) Unio,giganteus. Mississippi. Dr. Mitchill^s collection. 



(k.) Deeply folded. Maj. DelojieWs collection. 



(/.) With the cardinal tooth obhque. Mr. Collinses col- 

 lection. 



Variety (c.) has the beaks projecting and recurved : ci- 

 catrices deep ; prin^jary tooth deeply sulcate ; lateral tooth 

 long, high, and crenulate. It approaches our Unio Undatus. 



The variety [i.) deserves particular notice. A single valve 

 sent by Professor Douglass to Dr. Mitchill, weighs fifteen 

 ounces. It is in every respect, a gigantic shell. The dis- 

 tance between the points of the two lobes of the cardinal 

 tooth, is one inch ; the length of the lateral tooth, three 

 inches ; diameter of the posterior cicatrix, one inch, and 

 its depth one fourth of an inch. This shell of which four 

 specimens were obtained by the N. W. Expedition, might 

 perhaps constitute a separate species under the designation 

 of Unio Giganteus. It is three times the size of the largest 

 Unio Crassus, mentioned by Mr. Say and M. Lamarck. 

 Three specimens. 



Diam. 2-9 Length, 4'8 Breadth, 7-2 inches. 

 3-0 4-6 7-0 



3'1 4'7 7'1 are preserve- 



ed in Dr. MitchilVs cabinet. Another specimen 



Diam. 2-9 Length, 49 Breadth, 7*0 and weigh- 

 ing fourteen ounces, is preserved in Gov, Gass^s collection, 

 Detroit. Hab. The Mississippi near Prairie du Chien. 

 Prof. Douglass. 



Variety {k.) has the Epidermis dark biownish red, and 

 the shell is deeply folded like U. Plicatus. Hab. Lake Erie. 



