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BR ACHIOPOD A. _ 3 Genera. 
Shell bivalve , adhering to marine bodies, either directly or by a tendinous cord. 
Orbicula. — Shell suborbicular, inequivalve; without any apparent hinge: lower valve 
very thin, flat, adhering to marine substances; the upper valve subconical, the 
summit more or less elevated. 
[I have not been able to meet with any shell agreeing with the above description.] 
Terebratula. — Shell inequivalve, regular, subtriangular, attached to marine bodies by 
a short tendinous pedicle; the beak of the larger valve produced, often curved, 
perforated at the summit by a round hole, or by a notch : hinge with two teeth ; 
two nearly osseous, slender, elevated, forked, variously ramified branches rise 
from the disk of the small valve, and serve as a support to the animal. 
(1) Shell smooth, without longitudinal strive or furrows. 
Plate XIII. Fig. 5 T. vitrea- (Anomia vitrea. — Gmel ) 
(2) Shell striated longitudinally. 
Plate XIII. Fig. 4. T. psittacea. (Anomia psittacea. — Gmel.) 
Lingula. — Shell subequivalve, flattened, ovate-oblong, truncated at the summit, rather 
pointed at the base, elevated on a fleshy tendinous pedicle, fixed to marine bodies : 
hinge without teeth. 
Plate XIII. Fig. 6. L. anatina. (Patella unguis. — Linn.) 
(a) Inside of ditto. 
