122 Mr. Barnes on the Genera Unio and Alasmodonta. 



side, elevated, and recurved, with the ligament passing be- 

 tween them ; anterior lunule lortg-heart-shaped, and sepa- 

 rated by a slightly elevated heel ; hinge margin depressed, 

 between the beaks; basal margin waved and rounded be- 

 hind, compressed in the middle, angulated before; epider- 

 mis horn-color, exhibiting a light yellowish green where the 

 surface is worn or rubbed, wrinkled and finely striated trans- 

 versely ; surface glabrous. Cardinal teeth deeply sulcated 

 and crenated ; lateral teeth two in each valve ! internal or 

 lower one of the left valve small, but distinct and elevated, 

 and both marked with fine dotted striae. Muscidar impres- 

 sions deep, posterior one rough. Naker pearly white. . 



Remarks. — This shell, as will be seen by its dimensions, 

 has a more globose form than perhaps any other Unio. It 

 will stand erect on the posterior side, and in this position 

 has something of a pyramidal appearance. 



Variety [a.) Shell less, very slightly compressed, anterior 

 lunule much flattened, and the separating heel more eleva- 

 ted. No posterior lunule; transverse wrinkles deeper; 

 hinge bent to nearly a right angle. Teeth somewhat com- 

 pressed. Naker, pink or flesh colored ; surface polished 

 ^nd iridescent. 



Diam. l-O Length, 1-4 Breadth, 1-6 



Dr. MitchilVs Cabinet. 



Remarks. — This shell diflfers in so many particulars from 

 the former that we might have given it a different specific 

 designation, had we not been averse to doing that in the case 

 of solitary specimens. The double lateral tooth of the left 

 valve is distinct. 



C a. inside. 

 5. Unio Cornulus. Fig. 5. < b. outside. 



( c Posterior slope. 

 Shell sub-orbicular, divided longitudinally by a regular 

 row of large, distant tubercles. 



Hab. Fox River. Schoolcraft, 



My Collection. 



Diam. 1-0* Length, 1-7 Breadth, 1-6 



* Exclusive of the horns. 



