ORBICULA.—P are I. 
cular, and the vertex and subincumbent slit are nearly cen- 
tral; but when attached to a sloping or declivitous sub- 
stance, the vertex is pressed to one side, and the slit of 
the under valve follows the same direction. 
Species 2. (Mus. Cuming.) 
OrsBicuLa ANTILLARUM. Ord. testé ovato-orbiculari, de- 
presso-convecd, subtiliter radiatim striatd, striis irre- 
gularibus, subcorrugatis, vix clathratis, vertice subpos- 
teriori. 
Tue West Inpta Orpictta. Shell ovately orbicular, 
depressly convex, finely radiately striated, strice irre- 
gular, somewhat wrinkled, scarcely latticed, vertex 
rather posterior. 
D’Orsreny, Moll. Hist. Cuba, 1853, p. 368, pl. 28, f. 
34 to 36. 
Hab. Cuba, Martinique. 
Mr. Cuming possesses specimens of O. Antillarum, both 
from Cuba and Martinique, in all of which the vertex is 
inclined more posteriorly, while the shell is less regularly 
striated and less cancellated than in the Eastern O. stella ; 
but the shells are wonderfully alike in general aspect. 
Species 3. (Mus. Cuming.) 
ORBICULA LAMELLOSA. Orb. testd corned, fusca, subor- 
biculari, depressd, lamellis tenuibus elevatis concentricé 
rugosa, vertice postico, levigato. 
THE LAMELLATED OrBIcULA. Shell horny, brown, nearly 
orbicular, depressed, concentrically roughened with 
thin raised lamelle, vertex posterior, smooth. 
BroperipP, Pro. Zool. Soc. 1833, p. 124. 
Hab. Tquiqui and Bay of Ancon, Peru; Cuming. 
This very characteristic species, as related by Mr. Bro- 
derip, was found by Mr. Cuming in groups, the specimens 
being in many instances piled in layers one over the other 
on a sandy bottom, at a depth ranging from five to nine 
fathoms. At Ancon they were found attached to dead 
shells, and also clinging to the wreck of a Spanish vessel 
of about three hundred tons, that went down in the bay 
about ten years before. ‘The sunken timbers, for the 
sheathing was gone to decay, were covered with these 
shells, much in the same way that beams on land are 
sometimes infested with parasitic Fungi. At Iquiqui they 
were taken adhering to a living Mytilus. 
Species 4. (Fig. a, 6, Mus. Cuming.) 
OrpicuLa Layis. Ord. testd ovata, corned, solidiusculd, 
rufescente-fulvd, levigatd, undique superficialiter mal- 
leatd, posticé tumido-elevatd, vertice subobtuso, anticé 
depressa. 
THE smMooTH OrpicuLA. Shell ovate, horny, rather 
solid, reddish-fulvous, smooth, superficially malleated 
throughout, posteriorly tumidly elevated, vertex ra- 
ther obtuse, anteriorly depressed. 
Sowerby, Trans. Linn. Soc. 1822, vol. xiii. pt. 2. p. 468. 
pl. 26. f. la, 4, ¢, d. 
Hab. Conception, Chili (found attached to Myéili at a 
depth of six fathoms); Cuming. 
This species was first described by Mr. Sowerby, in a 
paper read before the Linnean Society in December, 1820, 
from a specimen attached to a grey flint pebble nearly 
coated by the root of an Jsis, of which the habitat was not 
known. Twelve years later it was found attached to shells 
dredged by Mr. Cuming, as above noted, off Conception, 
Chili. It is a stout horny shell, with the surface smooth 
and faintly malleated. The vertex, which much inclines 
posteriorly, is conically raised, swollen, and rather obtuse. 
Species 5. (Mus. Cuming.) 
ORBICULA TENUIS. Ord. testa orbiculari, tenui, pellucido- 
corned, nitente, concentricée striatd, posticé elevatius- 
culd, vertice parvo, subuncinato, deinde ubique depressi, 
THE THIN OrsicuLa. Shell orbicular, thin, transparent- 
horny, shining, posteriorly a little raised, vertex 
small, slightly hooked, then everywhere depressed. 
Sowersy, Thes. Conch. vol. i. p. 366. pl. 73, f. 4. 
Hab. Chili; Cuming. South Australia. 
Compared with the preceding species, the shell of O. 
tenuis is thinner, rounder, and more depressed. The 
original group of specimens represented in our Plate was 
collected by Mr. Cuming on the coast of Chili. But Mr. 
Cuming possesses specimens of an Ordicula which appear 
to me to be in all respects identical with this from South 
Australia. 
Species 6. (Mus. Cuming.) 
OrsicuLa Cuminert. Orb. testd suborbiculari, crassius- 
culd, striis minutis hie illic interruplis radiata, 
postice tumido-conoided, vertice subobtuso ; carneo- 
alba, interdum obscure fasciatd et radiata. 
Cumrne’s OrBIcULA. Shell nearly orbicular, rather thick, 
rayed with here and there interrupted striz, pos- 
teriorly tumidly conoid, vertex rather obtuse; flesh- 
white, sometimes obscurely banded and rayed. 
BropenriP, Pro. Zool. Soe. 1833, p. 124. 
Orbicula strigata, Broderip. 
