358 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxm. 



margin. It must be rem.embered that this is still a chalimus, and in 

 the subsequent development of the genital segment these fifth legs 

 may become partially or even wholly concealed on the ventral surface. 



The large spherical sperm receptacles can be seen in the posterior 

 portion of the segment, just in front of the fifth legs. 



Abdomen half as wide as the genital segment, one-jointed; anal 

 laminae small, triangular, each tipped with four large setse, three 

 close together at the inner corner, and one removed a little distance at 

 the outer corner. Outside of the latter there is also a minute spine. 

 Appendages similar to those of the female, the second antennae some- 

 what larger, the terminal claw stouter and carrying an accessory 

 claw on its ventral surface. 



The adhesion pads at the bases of these antennae are reduced still 

 more in size, and might easily be overlooked unless sought for particu- 

 larly. The second maxillipeds are radically changed from the pad- 

 form of the female and are tipped with a stout claw, well curved, 

 which shuts down against a pair of corrugated cushions as in Panda- 

 rus. Swimming legs all biramose, the rami of the first three pairs 

 two-jointed, of the fourth pair one-jointed. But from the arrange- 

 ment of the spines and the indentation of the margins these fourth 

 rami are each evidently a fusion of two joints, and possibly become as 

 fully two-jointed in later development as in Pandarus. 



The number and arrangement of the spines and setaa are as follows : 

 First exopod 1,0; 4,111: endopodO,0; 0,111: second exopod 1,1; 4,V: 

 endopod 0, 1; 0, V: third exopod 1, 1; 3, V: endopod 0, 1; 0, V: fourth 

 exopod 1,0; 3, V: endopod 0, 1; 0, IV. 



Total length, 3 mm.; length of carapace, including lobes, 1.7 mm.; 

 width, 1.55 mm.; length of free thorax segments, 0.92 mm.; length 

 of genital segment, 0.56 mm.; length of abdomen, 0.4 mm. Color a 

 light yellowish white without pigment. 



Chalimus. — Female chalimi were secured in three different stages of 

 development, which have already been described under the ontogeny 

 (see p. 340). It only remains here to emphasize their specific charac- 

 ters. The smallest of the three is exactly the same length as the male 

 just described, but is in an earlier stage of development. The simi- 

 larity between the two is much closer than in the adults, and affords 

 a striking proof that they are really the two sexes of the same species. 

 The carapace of this female chalimus is almost exactly like that of the 

 male, its posterior lobes being long and well rounded, very different 

 from their shape in the adult. The frontal plates are also much more 

 prominent than in the adult female, and are like those of the male. 

 The eyes are visible in both sexes, are of the same size, and similarly 

 placed. 



Again, the second, third, and fourth thorax segments are visibly 

 free in this young female, and are remarkably like those in the male. 



