Page 385

             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
top
     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 setae are 0 ( -
            a.~~~~~~~~~~~~~~~~                                  - I,.
    and the spines 0-1-0    The basal joint bears the usual dorsal sense,
    organ at the base, and at-he distal end are a spine anteriorly and 'a
Itplumose sense-hair behind. The proximal joint of the dorsal ramus,
    bears four well developed setme, and sometimes a fifth, proximal, seta
    which is much smaller than the others. Its presence or absence seems
    to depend on no law, asit is either present or absent in specimens of
all
    ages and both sexes and may be present on one side and absent on the
    other side of the same individual. All setm are two jointed and densely
    plumose.
      The proportionate length of individual setas differs in my specimens
  fro      atrali as   g      b       The terminal sh I-         iL, Of-
---
    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 setm 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.
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