556 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 112 



are the conspicuously flattened distal article of the second antenna 

 and the footlike expansion at the terminal end thereof in B. campestris 

 (fig. 2,a,d). 



Other noticeable differences are: (1) The antennule is relatively 

 shorter than in B. mackini. It is about 60 percent of the length of 

 the basal article of the antenna, whereas in mackini it averages 

 85 percent of the length of the basal article. (2) The apophysis is 

 smaller and is about half the size of that of mackini. (3) The proxi- 

 mal article of the antenna of mackini presents on the median side of 

 the distal one-fourth a small swollen area or projection bearing 3 to 7 

 sensory cones, whereas in campestris such an eminence is lacking. 

 (4) The food-gathering spines on the median border of the endopodite 

 in mackini are relatively shorter, with heavier spinules, than those of 

 campestris. (5) The telson in both males and females of campestris is 

 about one-half the length of abdominal segment 6; in mackini it is 

 only about one-third as long. 



The females differ from any species previously described in the 

 lateral outpocketings of the ovisac (fig. 5,a,e), and in the large size of 

 the dorsal bosses of the thorax (figs. 16, 46). 



Linder (1941) called attention to the arrangement of the paired 

 dorsal sensory bristles on the thoracic segments of B. gaini and 

 B. coloradensis , where those of thoracic segments 4 and 9 are nearer 

 the middorsal line than the others. This arrangement occurs also in 

 B. mackini and in B. campestris. Linder also mentions "granulated 

 knobs" and "bulges," mostly lateral to the sensory bristles. 



In many species of Branchinecta a pair of delicate sensory bristles 

 occurs on the dorsum of each segment from the first thoracic to the 

 sixth abdominal. Each bristle is typically surrounded by a circular 

 area of low cuticular granules or verrucae. The bosses of B. campestris 

 correspond to these granular areas, which in this species are remark- 

 ably developed, more or less hemispherical, and covered with coarse 

 cuticular verrucae. The conspicuousness of the bosses is augmented 

 by their being placed, especially those of segments 6, 7, 8, 10, and 11, 

 on a bulge or welt of the body wall. The sensory bristle persists in 

 many; in some it appears to be absent, or at least is undemonstrable. 

 Very rarely one of the anterior bosses is paired, but nothing correspond- 

 ing to the more lateral and ventral thoracic lobes, such as are found in 

 B. packardi or in B. lindahli has ever been found. 



The thoracic bosses of the female of B. mackini have the same 

 arrangement, but are much less conspicuous because they are rela- 

 tively smaller and rise much less above the surface. 



It is difficult to give brief and satisfactory measurements for the 

 bosses, since they vary in size from segment to segment and from 

 specimen to specimen, and since the height on each side is different 



