Decollated. Cut off, as the apex in some shells. 



Decussated. With spiral and longitudinal lines intersecting, as the sculpture 



of some shells. 



Deflexed. Bent downward, as the last whorl in some snails. 

 Dentate. With points or nodules resembling teeth, as the aperture of some snails. 

 Denticulate. Finely dentate. 



Depressed. Flattened. As the spire in some snails. 

 Dextral. Right-handed. 

 Digitiform. Finger-like. 



Dilated. Expanded in all directions, as the aperture of a shell. 

 Dimorphism. With two forms or conditions. 



Dimyarian. Having two distinct adductor muscle impressions or scars, as in Unio. 

 Dioecious. Having the sexes in two individuals, one male and one female. 

 Distral. The farthest part from an object. 

 Discoidal. Shaped like a flat disk. 



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

 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 some Unios, and the 



aperture in some gastropods. 

 Efferent. Carrying out. 

 Elliptical. With an oval form. 

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

 Emarginate. Bluntly notched. 

 Encysted. Inclosed in a cyst. 



Entocone. The inner cusp on the teeth of the radula. 

 Entire. With even, unbroken edges, as the aperture of some shells. 

 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 Sphierium when the umbones are placed 



in the center. 



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 pelecypods. 

 Excavated. Hollowed out, as the columella of some snails. 

 Excoriated. Worn away, or rubbed off. 

 Excurrent. Referring to the siphon which carries out the waste matter of the 



body. 



156 



