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SPECIES XVIII. Truncilla triqueter (Unio 

 triqueter.} 



Shell slightly thick, very ventricose ; apices 

 prominent ; shape almost trihedral ; posterior part 

 very flat, a little tessellated, ventricose ; epidermis 

 of a deep olive colour striped with brown ante- 

 riorly ; borders and wrinkles flexuous in the mid- 

 dle ; nacre bluish white. Length f diam. ^ 

 axis f of the breadth. 



A species very remarkable and rare, which I 

 have observed only at the falls of the Ohio ; its 

 form is so singular, that it has received the vul- 

 gar name of snuff box ; I have not seen the ani- 

 mal, which I suspect differs somewhat from that 

 of the Unio ; breadth one and an half inches, la- 

 mellar tooth short, broad, and obtuse ; muscular 

 impressions slightly marked, the posterior one 

 very large, occupying nearly all that portion of 

 the face of the valves ; fossule very slight ; edge 

 or border slightly flexuous. 



SPECIES XIX. Truncilla truncata (Unio 

 truncata.) 



Shell slightly thick, somewhat ventricose, 



slightly square ; apices prominent ; the posterior 



face truncated ; epidermis olive ; edge and 



irrinkles flexuous posteriorly ; nacre bluish white. 



