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ECOLOGICAL STUDIES OF THE ENTOMOS- 



TRACA OF THE ST. LOUIS DISTRICT. PART I. 



DIAPTOMUS PSEUDOSANGUINEUS SP. 



NOV. AND A PRELIMINARY LIST OF 



THE COPEPODA AND CLADOCERA 



OF THE ST. LOUIS DISTRICT 



0. H. Turner 



DiAPTOMUS PSEUDOSANGUINEUS Sp. NoV. 



The form is closely related to Diaptomiis sanguineus 

 Forbes and Diaptomus conipedatus Marsh, both of 

 which it resembles in having a very rudimentary endop- 

 odite on the fifth foot of the male. If we ignore color, 

 it is almost impossible to differentiate the females of 

 this species from those of Diaptomus sanguineus Forbes. 

 The males, however, are quite distinct. The fifth foot is 

 quite different, as is also the armature of the male an- 

 tenna. The fifth foot of the male of this species is sim- 

 ilar to that of Diaptomus conipedatus Marsh but the 

 antipenultimate joint of the right male antenna, in ad- 

 dition to a hook, similar to but somewhat longer than 

 that of Diaptomus conipedatus Marsh, also bears a hya- 

 line flange similar to that of Diaptomus sanguineus 

 Forbes. 



Description of the female, {pi. 1, fig. 1; pi. 2, fig. 1). — 

 The female is about 2.00 mm. long and the widest portion 

 of the thorax is about 0.54 mm. wide. The reflexed an- 

 tennae extend to the distal extremity of the furcal setae. 

 Viewed from the dorsal aspect, the cephalothorax widens 

 gradually from the tip of the head to about the third 

 thoracic somite, from which point it gradually tapers 

 to the tip of the abdomen. Viewed from the lateral as- 

 pect the body slopes continuously upwards and back- 



