382 THE CHICAGO ACADEMY OF SCIENCES. 
Annular. Made up of rings. 
Anterior. The front or fore end. 
Approximate. Near together, as the umbones of some Unios (pl. xxi 
fig. 1). 
Aquatic. Inhabiting the water. 
Arborescent. Branching like a tree. 
Arched. Bowed or bent in a curve. 
Arcti-spiral. Tightly coiled, as some spiral shells (pl. xxx, fig. 7). 
Arcuated. Bent in a bow or arched, as the ventral edge of some bi- 
valves (pl. viii, fig. 1). 
Asphyxiating. Causing suspended animation; apparent death. 
Assimilation. Act of converting one substance into another, as the 
changing of food-stuffs into living bodies. 
Asymmetrical. Not symmetrical. 
Atrophied. Wasted away. 
Attenuate. Long and slender, as in some shells (pl. xxxv, fig. 1). 
Auditory. Connected with the hearing. 
Auricled. Eared, or with ear-like appendages. 
Basal. The bottom or lower part. 
Biangulate. With two angles. 
Bicuspid or bicuspidate. Having two cusps. 
Bifid. Having two arms or prongs. 
Bifurcated. Having two branches. 
Bilateral. With two sides. 
Bilobed. With two lobes. 
Bivalve. A mollusk with two valves or shells, as the Unio. 
Branchial. Referring to the lower or ventral siphons in Pelecypods. 
Bulbous. Swollen. 
Byssiferous. Attached by a byssus, as in some Unios. 
Calcareous. Composed of carbonate of lime. 
Callosity. A hardened and raised bunch, as the callus on the colu- 
mella of some shells (pl. xxxv, fig. 9). 
Callus. A deposit of shelly matter. 
Calyculate. Cup-like, asthe umbo when separated from the rest of the 
shell by a distinct mark, as in Calyculina. 
Campanulate. Formed like a bell. 
Canaliculate. Resembling a canal, as the deep sutures in some shells 
(pl. xxxv, fig. 9). 
Cancellated. Formed of cross-bars, as the longitudinal and spiral 
lines which cross in some shells. 
Cardiac pouch. Containing the heart and placed near the umbones of 
the shell. 
Carinate. Keeled (pl. xxvi, fig. 5). 
Cartilaginous. Like cartilage. 
Caudal. Tail-like, or with a tail-like appendage. 
Cellular. Made up of cells. 
Cerebral. Pertaining to the brain. 
Channeled. Grooved or formed like a channel. 
Chitinous. Formed of chitin, as the radulz of snails. 
