PLEUROCERA. 75 



another fiir within, near the base. Aperture small, subrhomboidal, 

 Avhitish Avithin, three bauds visible in the interior; columella nearly 

 straight, a little thickened, outer lip very much curved, auger-like; 

 sinus narrow, recurved. 



Habitat. — Tennessee. 



Diameter, -38 of an inch (10 millim.) ; length, -SO of an inch (20 

 millim.). Length of aperture, '32 of an inch (8 millim.); breadth of 

 aperture, -IG of an inch (4 millim.). 



Observations. — A fine symmetrical species, which is, perhaps, most 

 nearly allied to JI. vestita, Conr. ; from that shell it differs in being less 

 ponderous, more acute in its outline, and in its flat whorls, the 

 JI. vestita being angulated below the middle; it has also a double 

 band, while vestita has a single one. From 31. elcvata, Say, it differs 

 by its less slender outline, its want of "thread-like carina;" on the 

 whorls, and its lines of growth are more curved, more elevated and 

 more distant; differs from JI. .spinalis. Lea, by not having carinated 

 whorls, by its more delicate color, and it has not the superior part of 

 the whorl darker than below, as described in JI. spinalis. — Anthony. 



Figured from the type. This species is very close to Thorn- 

 tonii, Lea, but its outline is narrower. It ma}' also be com- 

 pared with infrafasciatum, but differs in having more acutely 

 carinated whorls and a longer, more distinct fuse. The two 

 narrow bands are present in all the specimens I have examined. 



19. P. Postellii, Lea. 



Tnjpanostoma Postellii, Lea, Proc. Acad. Nat. Sni., p. 171, 1SG2. Jour. Acad. Nat. 

 Sci., V, pt. 3, p. 2SG, t. 36, 1". 110. Obs., ix, p. 108. 



Description. — Shell carinate, pyramidal, rather thick, horn-color; 

 spire regularly conical; whorls eight, flattened, the last rather small; 

 aperture very small, rhomboidal, whitish within ; outer lip 

 acute, very sinuous; columella thickened below and very 

 much twisted. 



Habitat. — Tennessee River; J. Postcll : North Alabama; 

 Prof. Tuomey. 



Diameter, -35 ; length, -S.") of an inch. 



Observations. — I have from ^Ir. I'ostell eight si)eciniens, 

 and from Professor Tuomey, five. They vary very little, but most of 

 them are imperfect at the apex or outer lip. This species very closely 



