FAMILY OSTRACIDZ — ANOMIA 167 
T. caput-serpentis, Linn, Gould. (JT. septentrionalis, Couruovy, Bost. Journ. Vol. 2, p. 65. Pr. 
34, fig. 321 of this work.) Shell rather thin, semitransparent, ovate: upper valve truncated hori- 
zontally at the apex; foramen large, one side completed by the apex of the lower valve; surface 
with a downy epidermis, under which minute radiating striz. From under each tooth in the lower 
valve arises a thin process, curving a little inwards, whose extremities support an oval partially 
twisted ring: margin of the shell crenate. Color, whitish. Length, 0:4; Width, 0:2. Coast 
of Northern Europe, Maine and Massachusetts. 
T. psittacea, Gmel. (Goutp, Op. cit. p. 142, fig. 91. Px. 34, fig. 322 of this work.) Shell thin and 
fragile, subtriangular, narrowed above; the beak produced into a decurved horn: surface striated 
concentrically and in radii; foramen triangular. Color, brownish black or sea-green. Length, 
0°35; width, 0°25. Northern Europe, and Seacoast of Massacusetts. 
T. thalassina, Gouxp. 
SECTION 2. LAMELLIBRANCHIA. 
Anima adherent, enveloped in a bilobed mantle, varying in the number and dimensions of 
its apertures.” Mouth transverse, medial, concealed at the bottom of the mantle between 
two pair of appendices. Gills in the form of semicircular leaves, composed of two pair, 
one on each side of the body: vent posterior and medial. Suet composed of two valves 
connected by a hinge and ligament, and enclosing the animal. 
FAMILY OSTRACIDAZ. 
Animat with the mantle not adherent, entirely open except on the dorsal part, without tube 
or peculiar opening. Foot wanting or rudimentary. The two pair of gills united in a 
medial line. Sue.t inequivalve, inequilateral, irregular, more or less lamellar or foliated : 
hinge variable ; ligament internal or partly internal ; muscular impression single, sub- 
central. 
GENUS ANOMIA. Bruguwiéres. 
Animal with the edges of its mantle thin, and furnished with a series of tentacular filaments. 
Foot rudimentary ; the adductor muscle divided into three branches, the largest of which 
passes through an aperture in the lower valve, with a corneous opercle to attach itself to 
other bodies. Shell thin, often translucent: one valve convex ; the other flattened or con- 
cave, and perforated near the beak. Ligament of the hinge short and thick ; muscular 
impression tripartite. 
