10. 



shells. "When the inhabitant becomes known it may authorize the 

 formation of a new genus, but there appears no character in the 

 conformation of the shell that would readily distinguish it from 

 Fusus. — Say. 



Mr. Lea, upon instituting the genus lo, renamed Jluvialis 

 as fusiformis, Lea, in accordance witli a custom very usual 

 among naturalists, but very reprehensible. He has recently 

 done Mr. Say and himself the justice of restoring the original 

 name — an example worthy to be followed. 



A young, very dark colored specimen of this species, Mr. Lea 

 named lo tenebrosa. He now agrees with me in considering it 

 to be a sj'nonyme of fluvialis. 



The following is the description, together with a figure from 

 the type specimen, of 



Fis. 28. 



lo tenebrosa. — Shell fusiform, rather thin, nearly black, smooth; 

 spire conical; sutures scarcely impressed; whorls 

 six, flattened; aperture irregularly pear-shaped; with- 

 in purple. 



Habitat. — Tennessee. 



Diameter, -48; length, -75 of an inch. 



Obscn-atio7is. — A single specimen only was brought 

 by Mr. Edgar from Tennessee. It is a small specimen, 

 and may be immature. After a good deal of hesitation I have deter- 

 mined to give it a place amoug the species. It seems to me to be very 

 distinct in color. The channel is more curved to the left and back- 

 ward than in Mr. Say's species. It has no trace of spines or tubercles, 

 and is dark all over. I do not know if it ever occurs banded. — Lea. 



The two accompanj-ing figures represent respectively^ smaller 

 and larger specimens than Mr. Lea's type. The ^'S- -^• 

 full grown shell is very frequently entirely smooth, 

 though it sometimes develops a few nodules 

 upon the periphery', but these do not attain 

 to the size of the " spines" which charac- 

 terize lo s2)inosa, and I have not found, 

 among numerous specimens, any that would 

 connect the two species. The color of Jluvialis 

 varies from yellow through various shades of light 

 and dark green and brown to black. Some specimens are 



Fie:. 30. 



