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Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume VIII (1888-1891)

Birge, Edward A.
List of crustacea Cladocera from Madison, Wisconsin ,   pp. 379-Plate XIII ff. PDF (7.9 MB)

Page 384

384      Wisconsin Academy of Sciences, Arts antd Letters.
                       DESCRIPTION OF FEMALE.
  Length up to 1.8 mm. but usually smaller.
  Measurements of average specimens.      s       s
                                         mm.      mm.       mm.
    Length      -      -     -     -     1.30       .82      .61
    Height   -     -      -     -         .80       .40      .27
    Antennule   -     -      -     -      .42       .35       .28
    Abdominal setae     -     -           .50       .41      .31
    Longest spine on carapace      -     1.05       -        .50
  The head is in some cases marked off from the body by a slight depres-
sion, not seen in young specimens, and often absent in older individuals.
The anterior outline of the head as seen from the side forms a straight
or slightly convex line from the attachment of the antennules to the eye,
where it passes by an abrupt curve into the dorsal margin. This mar-
gin is frequently continuous to the hinder end of the valves, and is
nearly straight in young specimens but strongly convex in old females.
Ventrally the anterior margin of the head terminates in a small pro-
jection to which the antennules are attached. The ventral margin is
continued into the labrum, and is entirely devoid of the leaf-like expan-
sion characteristic of Latona, Sars' organum affixionis. Above the inser-
tion of the antennae the valves are continued into small bilobed fornices,
resembling those of Latona but much smaller, and not continued to the
insertion of the antennules as are those of Latona. The head- as seen
from above is somewhat pyramidal in form.
  The carapace does not differ greatly from that of the Sididce in gen-
eral. It leaves the oral structures uncovered in front; it is straight or
convex dorsally according to the age of the animal; the ventral margin
is evenly rounded and passes into the nearly straight posterior margin
by a curve which forms no marked projection. The upper posteal angle
is well marked. The edge of the carapace is fringed with long plumose
setae, each set on a small elevation. At the lower posteal angle are placed
three setae, much longer than the others. They are often longer than
the carapace, and diverge from each other as they leave the shell, one
passing nearly straight backward and the others more outward. These
setae are longer in our species than in L. australis as figured by Sars.
The valves are not marked except by the braces (Stiitzbalken).
  Along the inside of the hinder edge of the shell, from the insertion of
the long setee to the junction of the valves, runs a row of fine spines
like those of Latona.
 The antennule consists of the basal part, the sense-hairs and the flagel-
lum. The first is short, oblong, freely movable. The sense-hairs num-

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