268 Mr. Barnes on the Genera Unio and Alasmodonta. 



over the ligament ; ligament large and prominent, passing 

 under the beaks ; anterior lunule depressed at the margin, 

 fuscous, broad-heart-shaped, longitudinally waved ; hinge 

 margin depressed between the beaks ; posterior slope car- 

 inate ; epidermis yellowish olive, becoming chesnut brown 

 on the umbones ; rayed with green, more conspicuous in 

 young specimens ; in old ones the dark chesnut brown 

 covers the whole and conceals the rays; surface smooth and 

 shining, reflecting the face of the observer; young shells 

 are splendent, having a much stronger lustre on the outside 

 than on the inside ; cardinal teeth broad, prominent and 

 obliquely flattened ; lateral teeth broad, elevated and ter- 

 minating abruptly before ; cicatrices large ; cavity of the 

 beaks unusually large ; naker pearly white; surface smooth, 

 but not highly polished. 



Remarks. — There is a remarkable uniformity in the di- 

 mensions of the full-grown specimens of this species. This 

 shell is more capacious than any other of the genus hitherto 

 described. It most resembles the unio ovatus, but its great- 

 er capacity, darker color, its smooth,shining and rayed sur- 

 face will distinguish it without mistake. 



Variety (a) ahell broader, less ovate, nearly oval and 

 rounded on both sides. 



A fine large shell. It measures 



Diam. 2.3-2.8 Length 3.1—3.8 Breadth 4.1—5.4. 



Inhabits the Wisconsan. Mr. Schoolcraft. 



Variety (b) shell light green, rayed, compressed. 



Inhabits the Wisconsan. 



Variety (c) shell with the teeth slightly elevated ; cardi- 

 nal one formed by a serrated edge of the shell, and a slight 

 projection within. 



Inhabits Barbadoes Neck, N. J. near New- York. 



Mr. Bradhurst's Collection. 



Diam. 2.5 Length 3.5 Breadth 4.8. 



Variety (d) a shell from the Delaware approaches this 

 species. The form and colour are similar. It is however 

 less, the largest measuring scarcely 2.3 inches broad ; ma- 

 king the shell not more than one fifth the size of those de- 

 scribed above ; also the beaks and bosses are less promi- 



