Whenever possible, the name of the stream from which material was taken is given. When this is not possible, the term “tributary” is used. As a general rule, the tributaries are streams emptying directly into the river under which they are placed, and the only exceptions to this, I believe, are the tributaries of the Arkansas arising in the southeastern corner of the state. Stagnant ponds in the region drained by a stream have been classed as tributaries, even through they have no direct connection. The above method of classifying the water systems of the state will, very possibly, be found not the best for a final arrangement, but for a preliminary classification—and nothing more than a preliminary arrangement can be hoped for at present—it seems quite satisfactory. MISSOURI RIVER, _C. virilis_, (5?). Tributaries, _C. virilis_, (5?), (22), (20?); _C. diogenes_, (1); _C. immunis_, (1). KANSAS RIVER, _C. virilis_, (3?), (6?), (11?). Tributaries, _C. virilis_, (1), (3?), (6?), (11), (18), (20); _C. gracilis_, (2); _C. diogenes_, (2); C. immunis, (2); _C. immunis_, var. _spinorostris_, (2). WAKARUSA RIVER, _C. virilis_, (23). Rock creek, _C. virilis_, (14). Washington creek, _C. virilis_, (15). Coon creek, _C. virilis_, (16). Wildhorse creek, _C. virilis_, (17). Ward’s creek, _C. virilis_, (2); _C. immunis_, var. _spinorostris_, (1). Mill creek, _C. neglectus_, (1). Wildcat creek, _C. virilis_, (26); _C. neglectus_, (4). REPUBLICAN RIVER, _C. virilis_, (7); _C. neglectus_, (2). Sappa creek, _C. virilis_, (9); _C. neglectus_, (3). SOLOMON RIVER, _C. pilosus_, (1?). Tributaries, _C. pilosus_, (1?) SMOKY HILL RIVER. Big creek, or tributary to it, _C. simulans_, (2); _C. immunis_, (2); _C. virilis_, (8). SALINE RIVER. Bullfoot creek, _C. virilis_, (24). Spillman creek, _C. virilis_, (25). A tributary of Salt creek, _C. pilosus_, (2). OSAGE RIVER, _C. virilis_, (10); _C. rusticus_, (1). ARKANSAS RIVER, _C. virilis_, (4?). *Tributaries, _C. nais_, (1); _C. gracilis_, (1). Tributaries, _C. virilis_, (4?); _C. gallinas_, (3). *Coal creek, _C. nais_, (2). *Labette creek, _C. virilis_, (21). CHIKASKIA RIVER. Tributary, _C. virilis_, (9); _C. gallinas_, (2), (4). LITTLE ARKANSAS RIVER. Tributary, _C. gallinas_, (1). MEDICINE LODGE RIVER. Tributary, _C. simulans_, (1). LABORATORY OF ZOOLOGY AND HISTOLOGY, UNIVERSITY OF KANSAS. [Illustration] FOOTNOTES: [A] Harris, J. Arthur: Annotated catalogue of the crayfishes of Kansas. Kans. Univ. Quart., vol. IX, No. 4, October, 1900. [B] I am not sure, in a trip across country, which of the two creeks, which flow together in this vicinity, I examined.