Diaptomus Birgei. 17 



armed with fine serrulations on its inner margin. The inner 

 ramus is one-jointed, equalling in length the first joint of the 

 of the outer ramus. 



The left fifth foot of the male reaches slightly beyond the firs^ 

 joint of the outer ramus of the right. The basal joint is quad- 

 rangular, considerably shorter than the right basal joint. The 

 first joint of the outer ramus is about twice as long as broad. 

 The second joint is slightly longer than the first joint ; it is ex- 

 panded at base, where it is armed with fine hairs, and termi- 

 nates in a finger-like process bearing a falciform spine. The 

 inner ramus extends to about one-half the length of the second 

 joint. 



Length of female, 1.5 mm. ; male, 1.3 mm. 



The material in which this species was found was collected by 

 Professor E. A. Birge at New Lisbon, Wisconsin, and only a few 

 individuals were found. I have expected to find it in the collec- 

 tions from other Wisconsin localities ; but so far my search has 

 been without success. It is a clearly marked species resembling 

 the European D. gracilis Sars more closely than does any other 

 described American species. The characters of the fifth feet, 

 however, separate it from the European form. 



I have taken the liberty of naming this species in honor of 

 Professor Birge, to whose kind assistance and encouragement I 

 have been greatly indebted. 



Bipo?i, Wis. 



