Ruth Marshall

THE ARRHENURI OF THE UNITED STATES

tirely enclosed in the female, in the male usually open onto the posterior extension of the body. The females are oval in form and much alike; the males are smaller and vary greatly from each other and from the females. They are characterized by a posterior prolongation of the body of varying length and complexity called the appendix, at the end of which there is often developed an accessory sex organ, the petiole. The epimera are in three groups. The capitulum has the form of a shield with a wedge-shaped notch closed by a membrane. The genital cleft in the female is flanked by two large semicircular discs, from each of which extends a wing-shaped area covered with small acetabula. The male genital area, at the base of the appendix, has narrow plates forming an elliptical plate for the cleft, from which extend narrow wing-shaped areas. The palpi are short and stout, ending in a pincer formed by the fifth segment and a prolongation from the distal end of the fourth. The legs are relatively short and much alike throughout the genus; the last three pairs have swimming-hairs, and the fourth segment of the fourth leg in the male usually has a spur bearing a bunch of hairs.

New Species of Water Mites of the Genus Arrhenurus

About ninety genera of Hydrachnidae are now recognized, with some eight hundred species. About one-fourth of these species belong to the single genus Arrhenurus. Fifty-five have been described for North America, chiefly from the upper Mississippi valley. This paper adds one new species. The hydrachnid fauna of South America has received little attention. Only eleven species have been described, of which five are for the females only. Dr. F. Koenike, in two papers (1894, 1905), published descriptions of two species (A. corniger, A. ludificator) found in material sent to him from Brazil. Dr. C. Ribago (1902) described a single species from Colombia (A. oxyurus). Dr. E. von Daday (1905) described seven new species from material collected in Paraguay; these were designated A. anisitsi, A. apertus, A. meridionalis, A. multangulus, A. propinquus, A. uncatus, A. trichoporus. Dr. C. Walter, in a paper published in 1912, described one new species (A. fuhrmanai), from Colombia. The present paper adds six new species. Material from Asia has been very scanty. Twenty-two species of Arrhenuri have been recorded; of these eight are from Asia Minor, mostly species found also in Europe. The remaining species have been found in the islands of Ceylon, Java and Sumatra. This paper adds two new species from China. The author has been very fortunate in securing the material for the descriptions of the nine new species of Arrhenuri included in this paper, and thanks are extended to the collectors who generously contributed it. The greater part of the material was found in collections made in northern South America by the late Harriet B. Merrill, in 1908 and 1909, and now in the possession of Dr. E. A. Birge, of the University of Wisconsin, who kindly permitted the author to sort out the water mites. Professor A. S. Pearse, of the