Fresh-Water Shells. 201 



of the pillar mncli less prominent, and the color yellowish. After 

 ail, these species are so nearly allied, that no description, and 

 perhaps no figure will enable a person to determine any one of 

 them by itself. They must be learned by comparison, and by 

 interchanging specimens. But the difficulty does not end here. 

 It is no easy matter to assign the limits of the spei-ies. No one 

 presents a greater variety. The length of mature shells varies 

 from half an inch to an inch ; and it is remarkable that the largest 

 specimens are usually the most fiagile. The surface usually has 

 an uneven, unfinished, inelegant aspect, coated with mud ; but 

 occasionally we find the conformation of the shell perfectly regu- 

 lar, the c< lor a shining greenish hurn-color, and the sui face smooth 

 and beautifully reticulated with longitudinal and revolving lines. 

 It is then a very pretty, fragile shell. Tiie aperture is small in 

 proportion to the shell, generally rather contracted ; again, we 

 find the hp beginning to expand, and in some specimens received 

 from Vermont, which I sJippose to belong to this specie, the lip 

 is broadlv flaring. Young specimens might be confouniled with 

 L. iimbilicdta, L. desidiosa. L. niodicellus and L. ca'perata ; but a 

 liitle attention to the umbilicus, the aperture, the c^ilor, and the 

 revolving lines will enable us to di-tinguish them respectively, 

 The umbilicus is usually entirely obstructed by the overlayiug 

 callus ; but in some specimens it is partially open. 



Limnjs'a Catascopiu:.!. — ^Say.) 



Shell ovate, ?,trong, chestnut-brown ', whorh foiir, lori'^kled, can 

 vex, the last large; sutw-e deep ; opirture sicb-oval, half the length 

 of the shell. 



Shell rather large, ob'ong-ovate, ventricose, thick and strong ; 

 epideimis chestnut or brownish horn-color; whorls four or a little 

 more, forming a short, pointed spire, delicately but rather regularly 

 wrinkled by the lines of growth, and these are rendered somewhat 

 corrugated by obsolete revolving lines; last whorl constituting 

 nearly the whole shell, very much distended; suture deeply im- 

 pressed ; spire very short, acute at apex; aperture rather more 

 than half the length of the shell, sub-oval, very little narrowed be- 

 hind ; not dilated; right lip:simple, thick and regularly curved; 

 left lip having a thick, narrevv lnyer of enamel, and a rather slight 

 fold midway; umbilicus not open. Length /„• inch, breadth -^^ 

 ^ncb, divergence 60o. 



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