570 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviu. 



latter is much larger. In the fourth swimming legs the terminal joint 

 is longer, and the spines and seta? differ slightly in their relative length 

 and arrangement. In both the male and female the bases of these 

 spines are reinforced by semicircular plates fringed with small hairs. 



Total length 4-5 mm. Length of carapace 2.35 mm; width of same 

 2 mm. ; length of genital segment 0.75 mm. ; length of abdomen 1 mm. 



Nauplitis larva. — Body elliptical, widest at about the center; width 

 to the length as 3 to 5. Appendages projecting far beyond the body 

 margin and typical in form (fig. 36, p. 536). 



First antennas uniramous, terminating in two plumose setae; second 

 antennae and mandibles biramous; exopod four-jointed, endopod two- 

 jointed; each joint of exopod bearing a long plumose seta, while the 

 terminal joint of the endopod carries two setae. 



The median eye is placed very far forward and concealed beneath a 

 spot of pigment. The anal setae are flattened spoon-shaped, of good 

 length, and they project sidewise from the body instead of diagonally 

 backward. The color is a pale yellowish, with rust-colored pigment 

 distributed in five spots, a small area over the median eye anteriorly, 

 a large area on either side at the center, and a small area on either 

 side just in front of the anal setae or balancers. The pigment is com- 

 paratively faint and scarcely appears under a low power as it does in 

 other species. The anterior half of the body is very transparent and 

 shows the internal structure plainly. Total length, 0.4 mm. Width, 

 0.23 mm. 



Chalimus stage. — Carapace elongate-ovate or spindle shape, nar- 

 rower anteriorly; frontal plates narrow and inclined backward along 

 the front margin of the carapace. Posterior lobes small, turned 

 inward strongly, and with scarcely any sinus; posterior margin of 

 carapace squarely truncate. Eyes a little behind the center of the 

 carapace, large and prominent; frontal gland very large and occupy- 

 ing the whole of the anterior angle of the carapace. Free segment 

 much larger than in the adult, one-third the length, and more than 

 half the width of the carapace, its sides strongly convex. Genital 

 segment and abdomen at first fused and about the same width as the 

 free segment, but separating with the first moult, the abdomen several 

 times the larger. Anal laminae short and wide, and projecting diago- 

 nally sidewise rather than straight backward; the plumose setae very 

 short and stout. Both pairs of antennae and all the mouth parts pres- 

 ent but somewhat rudimentary, especially the second antennae, whose 

 terminal joint is little more than a small spine on the tip of the large 

 basal joint (figs. 46-50). 



The first two pairs of swimming legs are the only ones developed in 

 early chalimus stages, and they are worthy of notice from the fact 

 that the first pair is biramose; but the endopod is made up of a single 

 joint, which is very small and quickly disappears. Color the same as 



