List of Crustacea Cladocera from Madison, Wis. 
385 
ber about eight and are placed on the posterior side of the distal end of 
the base. The flagellum is attached to the base with a distinct suture. 
Sars calls it “ distinctly articulated ” in L. australis. Whether he means 
that there is a movable joint he does not make clear. In L. occidentalis 
there is simply a distinct suture. The flagellum is long, curved back¬ 
ward, tapers to a fine point, and is fringed with long straggling sense- 
hairs. These are far less numerous than in Latona. Most of them are 
on the anterior side of the antennale but at the tip they are attached to 
all sides. In this arrangement of the hairs the structure differs from the 
antennule of L. australis as figured by Sars. The sense-hairs are also 
longer than he shows them and the whole antennule is about twice as 
long, relatively, as that of L. australis. 
The antenna closely resembles that of L. australis. The basal joint is 
exceedingly stout, so that the branches look too small for it. The dorsal 
sames is bi-, the ventral tri-articulate. 
The 
set® are 
4 (5) - 7 
0 —i —4 
and the spines ^^The basal joint bears the usual dorsal sense 
organ at the base, and at the distal end are a spine anteriorly and a 
plumose sense-hair behind. The proximal joint of the dorsal ramus 
bears four well developed setae, and sometimes a fifth, proximal, seta 
which is much smaller than the others. Its presence or absence seems 
to depend on no law, as it is either present or absent in specimens of all 
ages and both s^exes and may be present on one side and absent on the 
other side of the same individual. All setae are two jointed and densely 
plumose. 
The proportionate length of individual setae differs in my specimens 
from L. australis as figured by Sars. The terminal setae of the dorsal 
ramus are little longer than the others in L. occidentalis. The seta of the 
second joint of the ventral ramus is as long as the largest on the distal 
joint and each is quite twice as long as any other seta on the branch. 
The post-abdomen closely resembles that of L. australis. It is short, 
fleshy, obtusely conical, and armed with nine very small super-anal den¬ 
ticles. The abdominal setae are two-jointed, plumose, each set on a 
fleshy projection. They are a little longer than those of L. australis. 
The terminal claws are strongly curved, and have two secondary teeth, of 
which the distal is the longer. 
The mouth parts and legs seem to resemble closely those of the other 
Sididce. No careful study of the legs, has, however, been made. They 
number six pairs, as in other Sididce. 
INTERNAL ORGANS. 
In the structure of the internal organs L. occidentalis agrees closely 
with L. australis , and I can add little to Sars’ account. The general ar¬ 
rangement of the organs of the head may been seen in the figures. 
25—A. & L. 
