140 



dull yellowish brown ; umbo much eroded, exhibiting a chalky 

 white stratum, then a dull wax yellow surface ; beak a little 

 undulated, hardly elevated above the general curvature ; hinge 

 margin forming a large angle with the base, being anteriorly ele- 

 vated into an obtuse angle, whence the edge descends almost recti- 

 linearly to the anterior margin, which is equally rounded with the 

 posterior margin. 



Length one inch and three-tenths ; breadth less than two inches. 

 Convexity less than seven-tenths. Inhabits Mexico. 



I obtained several specimens in a ditch beside the road betwee''^ 

 the Capitol and Tacubya. It is perfectly distinct from any 

 species of this countiy that I have seen. It cannot be the 

 A. glauca, Lam., as that shell is represented to have " Natibus 

 prommuMs." 



Anodonta imbecilis. — Transvei-sely oblong subovate, very 

 thin and fragile ; disks convex, green, with darker green obsolete 

 rays, and three obvious rays on and above the umbonial slope ; 

 hinge margin rectilinear, terminating before in an angle ; beaks a 

 little undulated and not elevated above the general curvature ; 

 from the anterior tip of the hinge margin the slope is rectilinear 

 to the anterior margin ; within bluish white, iridescent before ; 

 hinge perfectly rectilinear ; posterior margin rounded. 



Length, over one inch. Breadth, over two inches. Convexity, 

 three-fifths of an inch. Inhabits Wabash River. 



By these dimensions, it is evident that the present species is 

 proportionally broader than any other of our Anodontse. of the same 

 length. It does not appear to be common in this river, or it may 

 have been overlooked or rejected as a young Unio by our collec- 

 tors, without examination. On this account, perhaps, I have only 

 two specimens, of which the smaller is less than half the size of 

 the present. It may be a young shell, but if so, in .the adult 

 state it must be much elongated, inasmuch as its proportions are 

 now nearly those of the full grown cygriea, Linn. It cannot be 

 the elongata, Swainson, as the shape differs, and that is a thick 

 shell with prominent umboncs. 



Melania pluristriata. — Turreted; with numerous trans- 

 verse, elevated lines. 



Inhabits Mexico. * 



