North American Sj^ecies of Diaptomns. 173 



terminates 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. ; of male, 1.3 mm."* 



Marsh states, in connection with the original description, 

 that the material in which this species was found — collected 

 by Professor Birge at New Lisbon, Wisconsin — contained only 

 a few individuals, and that his own search for it in other 

 Wisconsin localities had been unsuccessful. He says also 

 that the species resembles the European species Z). [iracilis 

 more closely than any other American form. 



The description quoted above is the only literature on the 

 subject, and while a request for slides or specimens of the 

 species by Professor Marsh was kindly complied with in the 

 case of most of his species, to his own as well as my regret 

 he was unable to let me have either slides or specimens of D. 

 hirgei. 



Unfortunately,as Marsh says, but few specimens were found, 

 and further study of the species must consequently be deferred 

 until later collections shall afford an opportunity. 



Diaptomus mississippiensis Marsh. (PL XXXIII., Fig. 

 1-4.) 



Diaptomus mississippiensis, Marsh, '94, p. 15, PJ. I., Fio^. 1-3. 

 Diaptomus mississippiensis, Herrick and Turner, '95, p. 78, PI. 

 XLVII., Fig. 1-3. 



A medium-sized species. Body slender, widest about the 

 middle of the posterior third, the male a little more slender 

 than the female, and the Avidest part slightly farther forward. 

 Last two cephalothoraic segments indistinctly confluent; 

 suture between the first two distinct. Last cephalothoracic 

 segment, seen from above, not produced, but bearing a 

 minute obtuse spine pointing backward ; seen from the side 

 it is broadly rounded, with the spine in the middle, giving it 

 the form of a brace (--^— ■ — ■). First abdominal segment about 

 as long as the remainder of the abdomen (PI. XXXIII. , Fig. 

 4), with a short obtuse spine opposite the anterior margin of 



♦Description quoted from Marsh, "94. 



