166 



Lserved to differ very essentially from that common species. The 

 umbo and beaks of tlie jilicatus are very prominent and altogether 

 destitute of any small literations or divaricating lines, having only 

 the origin of one or two of the large undulations grooved upon it. 

 The primary teeth of the plicatus also are much thicker than those 

 of this species. 



I formerly considered this species, with much doubt, as distinct 

 from the undulatus of Barnes, and gave to it the name of heros, 

 but notwithstanding some differences, I have concluded, after a 

 more mature examination and comparison, that it may be with 

 propriety referred to that species. Barnes drew his description 

 and figure from a specimen then unique, belonging to the cabinet 

 of Mr. S. B. Collins, which was so eroded as not to exhibit the 

 ornamental tubercles of the umbo and beak. 



The dimensions of a fine specimen found by Mr. 0. Evans are, 

 length five inches, breadth over seven, and convexity two inches 

 and seven-tenths. 



It is not iincommon in Fox river, an arm of the Wabash, in 

 muddy and sluggish parts of the stream. PL 16. 



Unio abruptus. — Specific character. Subquadrate, truncate 

 before. 



Desc. Shell oval-quadrate, yellowish olive or brownish, slightly 

 radiated with blackish-brown narrow lines, which do not extend to 

 the base : umbo not very prominent, rounded, slightly compressed, 

 generally radiated with obscure greenish, and placed far back, 

 almost terminal : disk convex, anteriorly with a hardly raised, very 

 obtuse elevation, becoming obvious towards the margin and a little 

 prominent at the anterior basal angle : hinge margin a little de- 

 pressed, so as to form an angle with the disk, more acute towards 

 the umbo : ligament higher than the beaks : anterior margin trun- 

 cated by an almost straight line : basal margin very slightly con- 

 tracted : posterior margin very short, gaping considerably from the 

 middle of the base to the cavity of the hinge membranes : cavity 

 of the hinge membranes very obvious, rather wide, as long or 

 longer behind the beaks than broad : within white, or tinged with 

 very fine fulvous-pink, or salmon color ; posterior cicatrix profound ; 

 smaller cicatrix rather large, oblique, arquated : palleal impression 

 hardly more prominent than the anterior cicatrix : cardinal teeth 

 thick, direct ; that of the left valve subtrifid : tooth plate rather 



