A NEW CRUSTACEAN, DIAPTOMUS VIRGINIENSIS, AND 

 A DESCRIPTION OF DIAPTOMUS TYRELLI POPPE. 



By C. DwiGHT Marsh, 



Of the United States Department of Agriculture. 



The species of Diaptomus in the United States are pretty well 

 known, inasmuch as collections have been made and examined from 

 practically all sections of the comitiy. Any material addition to the 

 number is not to be expected; hence considerable interest attaches 

 to anything that is distinctly new. Because, too, the species of 

 Diaptomus are so distinct, and in many cases 

 have such a definite geographical distribution, 

 it is especially important that the species 

 diagnoses should be as exact as possible. For 

 these reasons it seems wise to record the de- 

 scription of a new species recently found in 

 Virginia, and to publish the modifications 

 of the diagnosis of D. tyreUi which result from 

 the study of specimens from new locahties. 



DIAPTOMUS VIRGINIENSIS, new species. 



Of moderate size. The first cephalothor- 

 acic segment is somewhat longer than 

 the three following. The third and fourth 

 are much shorter than the second. The 

 last cephalothoracic segment is somewhat 

 produced laterally, and terminates on each 



side in a rather acute 



point. About midway 



on the posterior border 



of each lateral lobe is 



a minute spine (fig. 1). 



The general form of 



the cephalothorax is 



q 1 p Ti d fi r thft anterior ^'^- 2.-diaptomus virginien- 

 sienaer, me anx-enoi ^^^ abdomen of female, 



part narrow and almost x 445. 

 pointed. 



The first segment of the female abdomen (fig. 2) equals in length 

 the rest of the abdomen, including the f ureal rami; it is rather slender, 



Fig. 1.— Diaptomus vm- 

 GiNiENSis. Lateral 

 WING LAST Cephalo- 

 thoracic SEGMENT, 

 X445. 



Proceedings U. S. National Museum, Vol. 49— No. 2117. 



457 



