ROTELLA. 93 
thick, tuberculated; spire short; aperture narrow, terminating 
anteriorly in a short canal; outer-lip thickened, denticulated 
within, digitated without; columella spread over a portion of 
the body whorl, granulated. Obs. This interesting genus is com- 
posed of some neat little shells allied to Purpura, from which 
they are distinguished by the finger-like branching of the outer 
lip, and the granulations of the columella. Fig. 413, R. Horrida. 
RIGHT. See Dexrrat. 
RI'MULA. Defr. A genus consisting of a minute species of 
Emarginula, Auct. which has a fissure near the margin, but 
not reaching it. R. Blainvillii, fig. 243. 
RIMULI'NA. D’Orb. A genus of microscopic Foraminifera. 
RIS'SOA. Freminville. Fam. Ellipsostomata, Bl. Melaniana; 
Lam. Descr. Oblong, turrited, acuminated; spire long, consist- 
ing of numerous whorls; aperture round or oval, pointed poste- 
riorly, dilated anteriorly; outer-lip slightly thickened, emar- 
ginated; operculum horny. Obs. The Rissoz are small white 
marine shells, considered by some authors as resembling Mela- 
nie, but placed by Sowerby near the Scalarie. They are from 
the shores of the Mediteranian. Fig. 546, R. reticulata. 
ROBULINA. D’Orbigny. A genus of microscopic Forami- 
nifera. 
ROL'LUS. Montf. A genus composed of Conus Geographus, 
fig. 462, and other species, rather cylindricalin form, and having 
a coronated spire. 
ROSALINA. D’Orb. A genus of microscopic Foraminifera. 
ROSTELLA‘RIA. Lam. (From rostrum,abeak.) Fam. Alate, 
Lam. Siphonostomata, Bl. Descr. Turrited, fusiform, thick, 
smooth or ribbed; aperture oval, terminating anteriorly in a 
long canal, posteriorly, in a channel running up the spire; outer 
lip dilated, thickened, sometimes digitated, running up all or 
part of the spire, with a sinus near the anterior canal; inner lip 
smooth, spread over part of the body whorl and part of the spire. 
Obs. Hippochrenes is the name given by Montfort to the fossil 
species, which have the outer lip simple and very much dilated. 
R. curvirostris, fig. 402. 
ROTA’LIA. Lam. A genus of microscopic Foraminifera. 
ROTELLA. Lam. (A little wheel.) Fam. Turbinacea. Lam. 
Deser. Orbicular, generally smooth, shining; spire conical, de- 
pressed, short ; aperture subtrigonal; outer lip thin, angulated 
near the centre; inner lip spread over the under surface of the 
whorls, forming a thickened orbicular disc. Operculum horny, 
orbicular, spiral, with numerous whorls. Obs. The pretty little 
shells thus described, are found in seas of tropical climates. 
They are distinguished from other genera by their lenticular 
form and the orbicular callosity of the under surface. F ig. 357, 
R. vestiaria. 
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