13 



1 obtained several specimens in a ditch beside the road be- 

 tween the Capitol and Tacubya. It is perfectly distinct from 

 any species of tliis country that I have seen. It cannot be the 

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

 prominuli 



A. imbecUlis. Transversely 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 rectili- 

 near to the anterior margin: within bluish while, iridescent 

 before; hinge perfectly rectilinear — p jst:r ior 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 Anodontae 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 collectors, without examination. On this ac- 

 count, 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 cygnea, Linn. It cannot be the elongata, Swainson, as 

 the shape differs, and that is a thick shell with prominent 

 umboiies. 



HELIX. Linn. 



II. lucubrata. Shell suhglobosc depressed, reddish brown, 



jhed, subtranslucent: whirls over four, much wrinkled: 



much depressed, convex: suture moderate: beneath paler: 



umbilicus open, rather large: aprrtun nearly orbicular: labrum 



simple. 



Greatest width, one inch. Inhabits Mexico. 



Closelv allied to IT. irnrnnl> : . Nob., hut the umbilicus is 

 much 1 aperture is more accurately rounded^ the 



color i- nearly the same, excepting that in the present, it is of 

 per shade. 



