ANOMIA. MONOMYARIA. if 
margin, and forming a ridge, the whole external surface 
covered with projecting lamine; inside partly striated ; 
external surface covered with foliations. Structure of the 
hinge unknown. 
Spherulites foliacea. Plate VIII. fig. 5; and S. inequi- 
lobus. Plate IX. fig. 24. 
The latter species formed the genus Birostrites of Lamarck, but it has been 
recently ascertained to be only a cast of a Spherulite. Found at Aix in 
France. 
GRAND-DIVISION II. 
Ligament not marginal, but placed in a short hollow under the beak, always 
perceptible, and not forming a tendinous chord beneath. 
TRIBE I.—OSTRACEA. 
Iigament placed either interiorly or nearly so; shell 
regular m form, foliaceous and sometimes papyraceous. 
SUB-DIVISION I.—Ligament placed interiorly ; shell thin, papyraceous. 
Genus XIX.— ANOMIA. — Linneus. 
Generic Character. — Shell inequivalve, irregular, opercu- 
lated; under valve flattened with a large circular or ovate 
perforation near the hinge, and its edges turned back, 
through which protrudes a testaceous, or bony, straight, 
elliptical operculum or plug, with a dilated base, by which 
the shell adheres to extraneous bodies; upper valve the 
larger, concave and entire; ligament large, transverse, inter- 
nal, placed within the upper valve, at the umbo, and attached 
to a prominent, expanding appendage in the depressed valve; 
lower vaive with a single, orbicular, nearly central muscu- 
lar impression ; upper valve with three impressions, situated 
contiguous to each other, the largest is next the base of the 
shell, which is connected, by means of its muscle, with the 
plug, and the other two are also connected, by the medium 
of their muscle, with the single impression in the lower or 
flattened valve. 
Anomia lineata. Plate IX. fig. 13. 
The Anomiz are liable to considerable modifications of form, depending 
upon the shape of the substance to which they are attached. But, although 
the lower valve is in close juxtaposition with such substance, yet it does not 
adhere to it, but isattached simply by the testaceous plug or operculum. This 
appendage seems to be a testaceous prolongation of the abductor muscle of the 
animal, The shells of this genus will at once be distinguished from the Placuna 
