1278 



CRUSTACEA. 



rent genera in parallel lines, for comparison. Figures 1 a, 2 a, 3 a, 4 a, 

 5 a, represent the anterior antennae ; b, the posterior antennas ; c, the 

 mandibles ; d, the first pair of maxillae ; e, /, g, the three following 

 pairs of members. Figures 1 a, b, c, d, e, /, g, are of a Cypris; 2, 

 of a Gythere; 3, of a Cypridina; 4, of a Conchoecia; 5, of a Halocypris. 



The anterior antenna? are subterete organs, varying in number of 

 joints from three to seven, and are furnished with more or less setae, 

 especially at apex. In Conchoecia and Halocypris, in which the 

 number of joints is but three, one of the setae at apex is quite long, 

 and incrassated towards its extremity. 



The posterior antennce are of two types. In the fresh-water and 

 sea-shore species (Cypris and Cy there), they are rather slender, simple 

 subpediform organs, consisting usually of five joints, with setae at the 

 extremity and also a tuft, in the genus Cypris, at the apex of the third 

 joint; and in Cy there, two or three finger-like spines at apex, and a 

 very long slender two-jointed spinous process proceeding from the 

 apex of the second joint (fig. 2 b, PL 90). In the marine or oceanic 

 species, the organs are two-branched, and the basal joint is very stout, 

 being thick and subtriangular, sometimes as broad as long; it is filled 

 with muscles, for moving the rest of the organ, which is especially 

 fitted for natatory purposes. The terminal portion consists of an 

 oblong cylindrical joint, and a multiarticulate extremity of five to 

 seven short joints, furnished with long plumose setae. There is also a 

 second branch from below the apex of the large basal joint; this 

 branch is short and two-jointed. 



The five joints in the second type are represented normally as 

 follows. The large basal joint corresponds to the second, or to the first 

 two of the normal joints, as it bears the accessory branch, which is an 

 appendage normally to the second joint of an antenna or leg. The next 

 joint corresponds to the third in Cypris ; the last five or seven, form- 

 ing the multiarticulate extremity, to the fourth and fifth in the first 

 type. The setae at the extremity of these organs in Cypris pertain to 

 the fourth and fifth joints; and in Conchoecia to the representatives 

 of these joints. We have numbered the joints in correspondence with 

 these views, to aid the comparison with one another, and also with the 

 organs of the Cyclopoidea on Plate 70. 



The mandibles are also of two types. The one characterizing the 

 fresh-water and sea-coast species (Cypris and Cythere) has a denticu- 

 late apex, and bears a palpus on one side remote from the extremity, 

 in the usual way, the palpus (the proper termination of the mandi- 



