CLAUSES Pee 
NoTE FOR THE READER. — The descriptions, and measurements, in the 
book, and the definitions in this Glossary, presuppose the shells to be 
placed in the following positions : 
In Spiral Univalves, the apex above, the aperture below, and toward 
the observer. 
Bivalves, on the thin edge, with the umbones above, and the liga- 
ment on their left side. 
Acephala. _ Animals without heads. Ex., the oyster, mus- 
Sel, ete. 
Adductor (Muscle). The fleshy fibres which close and 
hold bivalve shells together. They are mostly one or 
two (Oyster, one; Unio, two). 
Anodonta. Toothless. Ex., the Anodont mussels. 
Aperture, or entrarice, or mouth, of univalve shells. The 
mouth of the shell is described as being entire, circular, 
lunate, semilunate, reniform, angular, sub-quadrate, long, 
wide, linear, dentate, emarginate, etc. The plane of the 
aperture may be longitudinal, transverse, or oblique. 
Apex. The tip of the spire, or umbo. It may be acute, 
obtuse, or sub-spiral. 
Base, of a univalve. It rests on the table in the position re- 
ferred to, and opposed to the apex. 
Bivalve. Having two valves. Ex., the clam. They may 
be compressed, cordiform, cylindrical, inflated, rostrate, or 
truncate. 
Branchial. Relating to the gills. 
Buccal plate. ‘The jaw of snails and similar mollusks. 
Cardinal tooth. ‘The large, central hinge tooth of Unios and 
many other shells. 
Carinate. Keeled. A longitudinal elevated line. 
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