Page:Scientific results HMS Challenger vol 18 part 2.djvu/840

1716 the capsule, at right and left, and are directed half backwards, half outwards (towards the frontal fissure between the valves, Pl. 123, figs. 1, 8a).

The phæodium exhibits in all Concharida the same characteristic shape, and represents a dark conglomeration of phæodellæ, filling up the anterior or oral half of the shell-cavity. Usually it is bilobed, divided into a dorsal and a ventral lobe or wing, which fills up the corresponding valve of the shell (Pl. 123, figs. 8, 9). The phæodium is commonly more voluminous than the capsule, and surrounds its anterior half, more rarely it encloses nearly the entire capsule (Pl. 124, figs. 6, 10). Its colour is usually olive, sometimes more greenish, at other times more brownish, in some species nearly black. The phæodellæ, or the roundish granules which compose the phæodium, exhibit the same shape as in all other (compare above, p. 1535). Sometimes peculiar rather oblong nucleated cells are scattered in great numbers between the phæodellæ, probably parasites or symbiontes (Pl. 123, figs. 7-9, 9a).

Definition.— with the lateral margins of the two valves smooth, without interlocking teeth.

Definition.— with the lateral margins of the valves smooth, without sagittal keel and without horns on the hinge.