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Two new species of Acanthocyclops Kiefer, 1927 (Copepoda: Cyclopoida: Cyclopinae) with pilose caudal rami from semiarid areas of Mexico. Zoological Studies 48(3): 380-393. Two new species of the freshwater cyclopoid copepod genus Acanthocyclops Kiefer, 1927 are described from ponds in the state of Aguascalientes, Central Mexico. The first species, A. caesariatus sp. nov. differs from its congeners by a unique combination of characters including 17 segmented antennules, the inner margin and dorsal and ventral surfaces of the caudal rami being strongly hairy, the coxal plate of leg 1 with rows of long spines, the caudal ramus 3.8 times as long as wide, and the dorsal seta about 1.5 times as long as caudal rami. The second species, A. marceloi sp. nov., has a relatively weak pilose pattern on the inner margin of the caudal rami, but these are covered with spinules arranged in symmetrical patches ventrally and irregularly on the dorsal surface; the length/width ratio of the caudal rami is 3.3. As in the other new species, the coupler of leg 1 is armed with spinules, but with a different pattern. Both new species resemble other forms with 17 segmented antennules and hairy caudal rami such as the North American A. carolinianus Yeatman and the European A. gordani Petkovski. The discovery of these new species in Central Mexico, which are both related to Nearctic forms, seems to be a result of radiation of these northern forms into Neotropical areas; the diversity of this genus in Middle America is underestimated and deserves further study. Inglés