10 G. o. SAES. [No. 8. 



the body. Those limbs, which admit of being partly extended 

 from the shell, are only the two pairs of antennae and the 1st 

 pair of legs, occasionally also the caudal rami. Besides, in the 

 male the prehensile palpi of the 2nd pair of maxillae and the 

 copulative organs may at times — during copulation — be found 

 exserted beyond the edges of the shell. All these parts are, on 

 the other hand, readily withdrawn within the shell, in which 

 case the valves close hermetically over the animal. 



The eye (see PI. IV, fig. 1), located at the frontal part of 

 the animal, just above the base of the upper antennae, exhibits the 

 structure characteristic of the greater part of Cyprididae, consisting 

 of a single mass of dark pigment, from either side of which a 

 clear refracting body of very delicate consistency is seen to 

 project. It would seem to be to some extent movable by the 

 aid of several muscular bundles originating from the inner face 

 of the valves and converging to the organ. 



The upper antennae (PI. Ill, fig. 1, PI. IV, fig. 1) are com- 

 posed of a thickish, muscular basal part, and a narrow cylindric, 

 flexible terminal flagellum. The basal part consists of 2 less 

 distinctly defined segments, the first of which is very massive, 

 of an irregular oval form and supported by several chitinous 

 stripes partly anastomosing with each other; anteriorly it bears 

 a single unciliated seta and posteriorly two similar but consider- 

 ably longer setae originating close together and diverging pos- 

 teriorly. The outer segment of the basal part is rather small 

 and at the end anteriorly provided with a short bristle. The 

 terminal portion of the antennae, which is very movably articu- 

 lated to the basal part, nearly equals the latter in length and 

 is composed of 5 articulations, the first of which is much the 

 largest, the others successively diminishing both in length and 

 breadth. They bear both anteriorly and posteriorly slender nata- 

 tory setae, disposed in pairs, and considerably increasing in length 

 towards the extremity. These setae form together a dense 

 fascicle, which during the swimming motion of the animal admits 

 of being spread to a certain extent.. 



The lower antennae (PI. Ill, fig. 2, PI. IV, fig. 1), originating 



