CALTGID.E. 201 



considered by some authors* as imperfect articulations. 

 One on each side extends from the notch at the termina- 

 tion of the narrow frontal plate to the sinus at the posterior 

 part of the carapace, dividing it into two lateral segments, 

 while a third runs across the centre of the body, connect- 

 ing the other two, and forming an upper and a lower 

 central segment. The upper, or anterior, may be called 

 the cephalic, and the lower the thoracic region of the 

 carapace. The former contains, attached to it, the an- 

 tennae, eyes, organs of mouth, and foot-jaws ; the latter 

 the first three pairs of natatory feet. 



The narrow plate, mentioned above as visible on the 

 anterior edge of the carapace, is sometimes very distinct, 

 and is prolonged laterally to a somewhat sharp point, 

 which is detached from the margin of the carapace, and 

 covers the insertion of the antennae. In tracing the parts 

 of these little creatures analogous to the parts belonging 

 to the higher Crustacea, we might consider this plate, 

 with its lateral prolongations, as the representative of the 

 first pair of antennae, here reduced to a single joint, and 

 inimoveably fixed to the carapace. 



The real antennas, (t. XXXIV, f. 5 b], corresponding to 

 the second pair in the higher orders, are very short, and 

 composed of two joints. The basal joint is inserted upon 

 the edge of the carapace, immediately beneath the ter- 

 minal point of the frontal plate. It is flattened in shape, 

 and the upper edge is beset with short setae. The apical 

 joint is narrow, nearly cylindrical in form, about two thirds 

 of the length of the preceding, and is terminated by 

 several short hairs. In many of the species we perceive, 

 on the frontal plate, near its free extremity on each side, 

 and on the inferior surface, a remarkable organ (t. XXXIV, 

 f. 5 a], consisting of a thin, nearly circular membrane, 

 attached by its central portions, and in form of a cup, 

 approaching somewhat in appearance to the sucking-disc 

 of the Argulus. These were considered by Midler as the 



* Pickering uiul Dana, loc. cit. 



