384 THE CHICAGO ACADEMY OF SCIENCES. 



Distal. The farthest part from an object. 



Discoidal. Shaped like a flat disk (pi. xxviii, fig. 25). 



Diverging. Separating from each other, as the cardinal teeth in some 

 Unios (pi. xviii). 



Diverticulum. A pouch or hole, as the pouch containing the radula, 

 or that containing the dart in helices. 



Dormant. In a 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 seme Unios, 

 and the aperture in some gastropods. 



Efferent. Carrying out. 



Elliptical. With an oval form (pi. xii, fig. 5). 



Elongated. Drawn out, as the spire of a shell (pi. 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 

 (pi. 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 Sphcerium when the umbones 

 are placed in -the center (pi. xxvii, fig. 3). 



Equilibrating. Balancing equally. 



Equivalve. With both valves of the same size and shape. 



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 (pi. 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. 



Fasciculus. A little bundle. 



Flagellate. Animals with a flagellum or lash. 



Flexuous. Formed in a 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. 



