522 Wisconsin Academy of Sciences, Arts, and Letters. 
1895. Arrenurus caudatus Koenike, Xordamericanische Hy- 
drachniden, Abhandlung des 11 aturwissenschaftlichen 
Vereins zu Bremen, Bd. 13, S. 184. 
1895. Arrenurus caudatus Piersig, Beitrag zur Kenntnis der 
in Sachsen, etc., Diss. S. 58. 
1896. Arrenurus caudatus Koenike, Holsteinische Hydrachni- 
den, Forschungsbericht IV der Ploner Station, S. 
212 . 
1896. Arrenurus caudatus Pisarovic, Zur Kenntnis der Hv- 
draehniden Bohmens, Sitzungsbericht, etc., S. 3. 
1897. Arrenurus caudatus Piersig, Deut. Hydrachniden, 
Heft 22, Lfg. IV, S. 285-288, Pig. 74. 
1899. Arrenurus caudatus Thor, Tredie Bidrag til Kunds- 
kaben om Horges Hydrach., S. 24, PI. IX, Fig. 88. 
1901. Arrenurus caudatus Piersig, Das Tierreich, 13 Liefer- 
ung. Hydrach. und Halacaridae, S. 87-88. 
1902-3. Arrenurus caudatus Soar, A Few Words on Fresh¬ 
water Mites, Trans, of the Edinburgh Field Natural¬ 
ists’ and Microscopical Society. 
This species, described so often by Eiuropean hydrachnologists, 
has been found but once by the writer, although many collec¬ 
tions have been made during the past ten years in various parts 
of Wisconsin and elsewhere. But a single individual was 
found; this was in Mud Creek, the inlet of Lake Spooner, near 
Spooner, Wis., on July 1st, 1903. It was at once recognized 
by its bright colors and its general conformity to the detailed 
figures of Piersig and Koenike. The area near the end of the 
body and the anterior part of the appendage was deep blue; 
there were brownish blue bands on the front part of the body, 
while the remaining areas were pale orange, and the legs bluish 
green. The entire length was 1.26 mm.; the greatest width, 
which is in the middle of the body, is 0.7 mm. It is readily 
distinguished from other Arrenuri of the sub-genus Megalurus 
by the shape of the appendage. This is constricted at the base, 
broadest in the middle where there is a slight hump, and nar¬ 
rowed at the end. Here it is slightly indented; on either side 
of the incision are two slight scallops, on this specimen not as 
pronounced as in Piersig’s and Koenike’s figures. In the last 
third are some peculiar structures. There is a small, some¬ 
what heart-shaped, bluntly pointed elevation (H 1 ) ; posterior to 
it is a pair of low rounded humps (H 2 ), between which is a de- 
