. Fresh-water biology. Freshwater biology. THE WATER-MITES (HYDRACARINA) 859 general resemblance between them is close. But the characters also seem to be very constant and few species are subject to marked variation. The accompanying synopsis will aid in placing speci- mens in the proper genus. The statements as to the numbers of species refer to North America only. The legs and the corresponding epimera are designated by Roman numerals, beginning with the most anterior, and the palpal and leg segments are referred to by Arabic numerals, numbering from the base outward. Thus, ep. Ill is the t
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. Fresh-water biology. Freshwater biology. THE WATER-MITES (HYDRACARINA) 859 general resemblance between them is close. But the characters also seem to be very constant and few species are subject to marked variation. The accompanying synopsis will aid in placing speci- mens in the proper genus. The statements as to the numbers of species refer to North America only. The legs and the corresponding epimera are designated by Roman numerals, beginning with the most anterior, and the palpal and leg segments are referred to by Arabic numerals, numbering from the base outward. Thus, ep. Ill is the third epimeron, leg seg. IV 4, the fourth segment of the fourth leg, and pal. seg. 5 the distal segment of the palpus. In most illustrations are shown the ven- tral surface, only the legs of one side, and the palpus, detached and more highly magnified; these are the characters most important and most readily observed. The arrangement of genera and higher groups here used is the same as adopted in a previous paper (Wolcott, 05). It is not in all respects satisfactory, but such a difference of opinion exists among students of the group in this regard that the author is not wilhng to accept any other system since proposed without himself working the whole matter over again. KEY TO NORTH AMERICAN FRESH-WATER HYDRACARINA 1 (6) Lateral eyes of the two sides close together in the median line and borne on a common eye-plate 2 2 (s) Pal. seg. 5 deeply set into 4, eye-plate long and narrow. Family Limnocharidae 3 3(4) Without swimming-hairs Limnochares LiLtTeille lygd. A very large clumsy red mite with soft body, variable in form but in general rectangular, found in pools in bogs and swamps. Length 3.5-4 mm. One species, generally distributed and common at times. Fig. 1322. Limnochares aguaticus (Lin- naeus). Ventral surface, female. X 9- Inner surface, right palpus. X 95- (Mod- ified from Piersig.) 4 (3) With swimming-hairs Cyclothrix Wolcott 1905. Also red but oval and more constant in