* 
384 THE CHICAGO ACADEMY OF SCIENCES. i. 
Distal. The farthest part from an object. 
Discoidal. Shaped like a flat disk (pl. xxviii, fig. 25). : 
Diverging. Separating from each other, as the cardinal teeth insome 
Unios (pl. xviii). 
Diverticulum. A pouch or hole, as the pouch containing the radula, 
or that containing the dart in helices. 
Dormant. Ina state of torpor or sleep. 
Dorsal. The back. In bivalves the hinge portion, and in univalves 
the opposite to the aperture. , 
Ectocone. The outer cusp on the teeth of the radula. 
Edentulous. Without teeth or folds, as the hinge plate in some Unios, 
and the aperture in some gastropods. 
Efferent. Carrying out. 
Elliptical. With an oval form (pl. xii, fig. 5). 
Elongated. Drawn out, as the spire of a shell (pl. xxxii, fig. 6). 
Emarginate. Bluntly notched. 
Encysted. Enclosed in a cyst. 
Entocone. The inner cusp on the teeth of the radula. 
Entire. With even, unbroken edges, as the aperture of some shells 
(pl. xxvi, fig. 4). 
Epiphallus. A portion of the vas deferens which becomes modified 
into a tube-like organ and is continued beyond the apex of the penis; it 
frequently bears a blind duct, or flagellum. (Pilsbry.) 
Epithelium. All tissues bounding a free surface. 
Equidistant. Equally spaced, as the spiral lines on some snail shells. 
Equilateral. Equal sided, as in Unio or Sphzrium when the umbones 
are placed in the center (pl. xxvii, fig. 3). | 
Equilibrating. Balancing equally. . 
Equivalve. With both valves of the same size and shape. “i 
Eroded. Worn away, as the epidermis on some shells. \ 
Erosive. Capable of erosion. 
Escutcheon,. The region behind the umbones in opisthodetic pelecy- 
pods. 
Excavated. Hollowed out, as the columella of some snails (pl. xxxvi, 
fig. 10). 
Excurrent. Referring to the siphon which carries out the waste matter 
of the body. 
Exoskeleton. The outer skeleton; all shells are exoskeletons. 
Exserted. Brought out. 
Expanded. Spread out, as the lip of some shells. 
Falcate. Scythe-shaped. “i 
Fasciculus. A little bundle. ‘ 
Flagellate. Animals with a flagellum or lash. : v 
Flexuous. Formed ina series of curves or turnings, as the columella “= 
in some shells. ¥ 
Flocculent. Clinging together in bunches. (See anatomical portion 
for the application of this word.) 
Fluviatile. Living in running streams. 
Fusiform. Thick in the middle and tapering at each end. 
