39 
PcPA PLACIDA. — Shell dextral, cylindric-conic, pale yellowish 
horn color ; apex whitish, obtuse ; whorls six and a half, some- 
what wrinkled ; suture moderately impressed ; aperture unarmed, 
longitudinally oval, truncate a little obliquely above by the 
penultimate volution ; columella so recurved as almost to conceal 
the umbilicus ; labrum, with the exception of the superior portion, 
appearing a little recurved when viewed in front, but when viewed 
in profile, this recurvature is hardly perceptible ; umbilicus very 
narrow. 
Length over three-tenths of an inch. Inhabits Massachusetts. 
For this shell I am indebted to Dr. T. W. Harris, of Milton, 
from whom I have received many interesting species of our more 
northern regions. At first view it might be mistaken for the P. 
marginata, JVob., but it is quadruple the size, and the labrum is 
not reflected and thickened. 
Bulijius alternattjs. — Ovate conic, with alternate gray and 
brownish longitudinal vittae. Inhabits Mexico. 
Shell umbilicated, ovate-conic, with longitudinal lines, subequal, 
gray and light brownish vittae ; the brown is paler, almost 
approaching in some instances a drab ; the white vittac consists of 
more or less confluent, transverse, irregular lines, and small spots ; 
whorls about six, a little convex ; suture not profoundly impressed ■, 
labrum (in some specimens) with a thickened line or rib on the 
inner submargin j within white, with a perlaceous tinge. 
Length one and one-fifth of an inch. Greatest breadth seven- 
tenths. This species appears to be not uncommon in Mexico, as 
many specimens were sent me by Mr. Maclure ; but from what 
particular locality, I know not. 
B. UNDATUS, Brug. — Occurs in some parts of Mexico. I 
found a specimen on the road from Vera Cruz to the city. The 
late Mr. Elliott, of Charleston, presented to me a Bulimus which I 
described under the name of reses; but on comparing it to the 
present species, I think it may be considered as a variety } it is 
rather less ventricose, the longitudinal lines are very slender and 
pale, and the transverse lines much more distinct. It inhabits 
trees on the south part of Florida. 
B. SERPERASTRUS. — Elongate subovate, about six banded. 
Inhabits Mexico. Shell conic or elongate subovate, umbilicated ; 
whitish or white, with about six interrupted, more or less con- 
