ORBICULA.—Ptarte I. 
Hab. Central America (dredged at Payta, St. Elena, 
Panama, and Isle of Cafia, Guatemala, attached to 
the lower side of stones in sandy mud at low water, 
and in some instances at a depth of from six to 
eighteen fathoms) ; Cuming. Hcuador; D’Orbigny. 
Mazatlan (on various shells) ; Carpenter. 
Mr. Broderip’s O. strigata, which he did not describe 
along with O. Cumingii in the Proceedings of the Zoolo- 
gical Society, but as an afterthought when figuring the 
Orbiculeg in the Transactions, is a less worn state of the 
species, in which there are faint rays and bands of colour. 
The upper valve is calcareous and firm, of quite a different 
type to the horny species of Chili and Peru. The habi- 
tats, Malacca and Philippine Islands, given with this spe- 
cies by Mr. Sowerby, in addition to the above, are erro- 
neous. He probably mistook specimens of O. séella for it. 
Species 7. (Fig. a, 6, Mus. Cuming.) 
QORBICULA OSTREOIDES. Ord. testa ovatd, crassiusculd, 
rude convexd, interdum conoided, radiatim densé cor- 
rugato-striatd, striis prominentibus, hic illic tumidis 
et cancellatis, vertice subcentrali. 
THE OYSTER-LIKE Orgicuna. Shell ovate, rather thick, 
rudely convex, sometimes conoid, radiately densely 
wrinkle-striated, strie prominent, here and there 
swollen and caneellated vertex nearly central. 
Discina ostreoides, Lamarck, Anim. sans vert. 1819, 
vol. vi. p. 237. 
Orbicula Norveyica, Sowerby (not of Lamarck) ; 
Trans. Linn. Soc. 1822, vol. xiii, p. 468. pl. 26. 
f. 2 a, 6, ¢, d, e, f. 
Orbicula striata, Sowerby, Thes. Conch, 1846, vol. i. 
p. 366. pl. 73. f. 8. 
Crania radiosa, Gould. 
Orbicula Evansii, Davidson. 
Hab, North-west Africa? (in crevices of brown oxide of 
iron). 
This species was originally named by Lamarck from a 
specimen sent to him in 1819, by Mr. James Sowerby, 
father of Mr, G. B. Sowerby, who described it the follow- 
ing year in a paper read before the Linnean Society as 
Orbicula Norvegica. He had then discovered it in abun- 
dance in the crevices of a quantity of ballast stone, brown 
oxide of iron, used in the neighbourhood of Lambeth for 
mending the roads. In Mr. G. B. Sowerby’s monograph, 
many years later, in his son’s ‘Thesaurus Conchyliorum,’ 
he makes no mention of his mistake in having described 
this species in the Linnean Transactions as O. Norvegica, 
and names it striatus for the first time, although he bears 
testimony to its being the species on which . Lamarck 
founded his genus Discina. 
I am of opinion that Mr. Davidson’s-O. Hvansii, the 
original type of which is before me, is a specimen in which 
the vertex of the upper valve and corresponding disk of the 
lower valve are more central than usual, owing to its po- 
sition of attachment ; and the under valve is more convex 
for the same reason. When adhering to a convex crevice, 
as in the specimen of iron-stone represented in our Plate, 
the lower-valve is more concave and the disk more central.” 
The locality, Bodegas, California, given by Mr. Davidson 
with O. Zvansiit on Mr. Cuming’s authority, must, I think, 
be a mistake. The specimens are precisely like those con- 
tained in the crevices of ironstone, and are similarly dis- 
torted. 
