84 
fresh water shells it possesses the power of gliding along the sm- 
face of the water^ with the shell downward. 
This shell is something like T. reticulata^ but the sculpture is 
less profound^ and it has never any appearance of varices^ or iii- 
erassation of the labrum. 
Turritella impressa. — Shell dusky^ acute at the apex ) volu- 
tions six^ with about four acute^ impressed, revolving lines ; labrum 
not thickened, a slight indentation at its base, and a projecting 
angle within its middle. 
Inhabits the coast of Maryland. Length more than one-eighth 
of an inch. 
I have seen but two specimens of this species. The aperture 
is precisely similar to that of the preceding species. 
Turritella bisuturalis. — Shell thin, pellucid, small, conic ; 
whirls five, wrinkles almost obsolete, a revolving impressed line 
near the suture ) suture not deeply impressed ) spire gradually 
tapering, rather longer than the aperture ; aperture rounded at 
base, and perfectly entire. 
Length rather more than one-tenth of an inch. Inhabits Boston 
harbor. My cabinet. 
I am indebted to Mr. Aaron Stone for this small species of 
Turritella. It is distinguished from all others that I have seen, 
by the single impressed line, which revolves near the suture. 
Bulla solitaria. — Shell remarkably thin and fragile, pellu- 
cid, oval, narrowed at base, with numerous impressed revolving 
lines, and transverse very obtuse wrinkles ; aperture surpassing the 
tip of the shell ) spire none, substituted by an umbilicus ; umbilicus 
of the base none. 
Less than half an inch. Inhabits the southern coast of the 
United States. 
I found a specimen of this species of Bulla on the coast of 
Maryland, but have not seen another. It is probable that it is 
rare. It approximates to the description of B. hydatis, but it can 
hardly be the same, as it is more oblong than the species B. 
naucum agreeably to the figure in the Encyc. Meth., which spe- 
cies is referred to by Billwyn, as being of the same form with 
hydatis. 
Melampus bidentatus.- — Shell thin, fragile, dirty-brownish ; 
