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Skinner, Ernest B. (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XIV, Part I (1902)

Marshall, Ruth
Ten species of Arrenuri belonging to the subgenus Megalurus thon,   pp. [145]-Plate XVIII ff.

Page [145]

                    BY RUTH MARSHALL.
   The work upon the genus Arrenurus Duges has been carried
on fron4 the spring of 1893 up to the present time, with many
interruptions. Collections have been made at several places
in Wisconsin and one in -Massachusetts. This paper embodies
the results of the studies upon the species of the subgenus Mega-
lurus Thon, most of the work having been centered on this
  The Arrenuri form one of the most easily recognizable genera
of the Hydrachnidae. They form a, sharply defined, highly
organized and well differentiated group, very rich in speies
They are characterized by the possessession of a very hard,
transparent, porous in gumentan area of -which ise--parated-
on the back by a circular furrow from the rest to form the
so-called "dorsal shield"; and by great sexual diamorphism.
The females have a more or less rounded form and closely
resemble each other; while the imiales have a peculiar prolonga-
tion of the posterior end of the body, presenting numberless
modifications in the different species and offering the chief spe-
cific characters.
  Thon (1900) makes three subgenera of the Arrenuri. Petio-
lurus -embraces species in which the posterior appendage is
short, or altogether wanting and represented by humps on the
dorsal side of the body; and in which there is a peculiar and
characteristic structure, the "petiole," a small oblong
structure at the extreme posterior end of the body. Arrenurue
pustulator Muller is an illustration. Subgenus Micrurus has
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