Article III. — The North American Sp)ccies of Diaptomus. 

 By Frederick William Schacht. 



INTRODUCTION. 



The first published reference to that group of genera of 

 Entomostraca now known under the family name of Centro- 

 pagidee is contained in 0. F. Midler's "Entomostraca seu 

 Insecta testacea quae in aquis Daniae et Norvegiae reperit," 

 etc., published at Frankfort-on-the-Main in 1785, in which 

 paper certain copepod species now included under the genus 

 Diaptomus were treated under the general name of Cyclops. 

 Species of Diaptomus were later described by Jurine ('20) 

 under Monoculus, but the genus Diaptomus was first estab- 

 lished by Westwood ('36). Various names have since been 

 applied more or less closely to the generic group : Cyclopsina, 

 Milne-Edwards ('38); Qlaucea, Koch ('38); and Cyclops, 

 Nicolet ('48). 



The first American species of Diaptomus recognizably 

 described was D. sanguineus Forbes ('76). Later Dr. Forbes 

 ( '82a) described three additional species of this genus (sicilis, 

 leptopus, and stagnalis), and two new genera of Centropagidce 

 (Epischura and Osphranticum), with a single species of each. 

 Prof. C. L. Herrick's publications on the group began in 

 1877 and those of Marsh in 1891. A single species (D. 

 kentuckyensis) named by Chambers in 1881 is so imperfectly 

 described that its recognition is apparently impossible. Since 

 the publication of Underwood's " List of the described Species 

 of Fresh-water Crustacea from America North of Mexico" 

 ('86) the number of recognized North American species of 

 Diaptomus has increased from five to twenty-three. 



The literature of the genus previous to 1889 was widely 

 scattered and the synonymy greatly complicated, but the 

 comprehensive and careful "Kevision" published in that 

 year by de Guerne and Richard ('89b) has had the effect 

 greatly to facilitate its study. The most important recent 

 European contributions to a knowledge of the Centropagidce 



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