PLEUROCERA. 59 



Observations. — This is one of those species of Melanidce which we 

 have considered to belong to the group witli a regular channel at 

 the base, like the genus Fusus, but which really belongs to the 

 genus lo, having other characters difl'ering from Melania. It is nearly 

 allied to the species which I described as Melania nohilis* in the 

 Trans. Am. Phil. Soc, vol. x, pi. 9, fig. 48, from a single imperfect 

 specimen. It is a smaller species, and is not so fusiform, having a 

 shorter channel, which is not quite so much twisted, and the nodules 

 are not so large. The aperture is more than one-third the length of 

 the shell. — Lea. 



lo variabilis. — Shell smooth, raised, conical, subfusiform, 

 banded, deep purple or greenish; spire regularly conical; 

 sutures slightly impressed; whorls about nine, flattened, 

 angular in the middle ; aperture elougately rhomboidal ; 

 outer lip sharp and sinuous ; columella white or purple and 

 very much twisted ; canal long and narrow. 



Habitat. — Tennessee River, Alabama? Wm. Spillman, M.D. 



Diameter, -4:0; length, '88 of an inch. 



Observations. — A number were received from Dr. Spillman, but 

 they ai-e generally young, and the older specimens were much in- 

 jured in the delicate fuse and outer lip. It is a small, thin species, 

 with a well developed, nearly straight, channel. It seems to be a very 

 variable species, some individuals being of intense purple, nearly 

 black, while others are yellowish, with numerous bauds; others 

 again are greenish, without bands. Some are carinate towards the 

 apex, while others are free from carination. There is a disposition in 

 several to be tuberculate along the angle on the middle of the lower 

 whorl. Generally there is a light line along the upper part of the 

 whorls. The aperture is nearly one-half the length of the shell. — Lea. 



The four species xindulatum., excurattcm,, moniUfenim and 

 rohustum are mainly distinguislied by tlie following differ- 

 ences : — 



Undulatum is a stout, broadly conical shell, strongly angled 

 on the periphery and having large tubercles. The base is much 

 flattened. 



Ilobustum., with much the same general outline, is not much 

 angled on the periphery, with the inferior portion of the whorl 



• In transfcrrlnp: this to the genus lo, I tliluk it may properly be considered the type of 

 a group of the genus. 



