CONCHOLOGY. 85 
Shell. Thin, inequivalve, regular, subtrigonal; one of the 
valves larger and more dilated than the other, which is sometimes 
operculiform; hinge condyloid, in a straight line, and formed by 
two oblique articular surfaces in one valve placed between corres- 
ponding projections in the other. Inhabits the sea at the Zetland 
Islands. T'wo species are found in America. Thirteen living 
species. Thirty-eight fossil. 
Terebratula dilatata. Terebratula globosa. 
T. flavescens, T.. caput-serpentis. 
T. dorsata. T. psittacea. 
T. Vitrea. T. rotunda. 
T. dentata. T. pisa. 
T. sanguinea. 
T. septentrionalis.* T. truncata.* 
3. Genus Lingula. Pl. IX. 
Animal. Depressed, oval, somewhat elongated, inclosed be- 
tween two lobes of a mantle, slit throughout its anterior half, and 
having pectinated branchie adhering to the internal surface ; 
mouth simple, having on each side a long tentacular appendage 
ciliated in all its external edge, and rolling itself up spirally in the 
shell. . 
Shell. With an epidermis, subequivalve, equilateral, depressed, 
elongated, truncated anteriorly ; the summit median and posterior ; 
no trace of ligament; a long fibro-gelatinous peduncle fixing the 
shell vertically to submarine bodies ; muscular impression multiple. 
Inhabits the Indian Ocean. One species. 
Lingula anatina. 
CLASS IV. 
MOLLUSCA. 
Animals soft, inarticulated, furnished with an anterior head | 
projecting or salient ; most frequently with eyes and tentacule, or 
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