48 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



requisite, and the limitations of range in themselves point to a more 

 recent origin than the other groups of micro-crustacea; nor is it diffi- 

 cult to trace the connecting links in many cases. 



KEY TO THE FRESH- WATER GENERA OF THE CALANID^. 



I. Fifth feet of the female bi-ramose. 



a. Inner rami of all the swimming feet three-jointed. 



* Inner ramas of the right male fifth foot three-jointed, 



t Outer ramus of the right male fifth foot two jointed. L/iinnocalanus, 48 

 ft Outer ramus of the right male fifth foot three-jointed. 



Osphranticuin, 85 



** Inner ramus of the right male fifth foot reduced. . . . *Boeckella. 



&. Inner rami of the first swimming feet two-joiuted. . . . Diaptotuiis, 54 



c. Inner rami of all the swimming feet two-jointed Broteas, 80 



II. Fifth feet of the female uni-ramose. 



a. All the swimming feet with the inner ramus one-jointed. 



* Abdomen symmetrical, not prehensile in the male. . Heterocope, 80 

 ** Abdomen unsymmetrical, with prehensile appendages in the 



male Episcliura, 81 



b. First swimming foot with one-jointed inner ramus, the rest two- 



jointed Eurytemora, 49 



c. Swimming feet with three-jointed inner rami. 



* Fifth foot of the male one-branched. . . . Pseudodiaptonius, 53 

 ** Fifth foot of the male with one-jointed inner ramus. . . *Poppella. 



GENUS LIMNOCALANUS Sars. 1863. 



Cephalothorax six-jointed, slender, last segment never divaricate. 

 Abdomen in the female three- or four-jointed (not including stylets), 

 in the male five-jointed. Caudal stylets elongated with five setse. 

 First antennse 25-jointed, shorter than the body; in the right antenna 

 of the male a geniculate joint between segments 18 and 19. Second 

 pair of maxilliB, strong, eight-jointed, last joint unguiculate. Feet 

 bi-ramose, those of the first four pairs with three-jointed rami. Outer 

 ramus of fifth feet in the female three-jointed, with a claw-like process 

 from the second segment; inner ramus like those of the other feet. 

 The outer ramus of the right foot of the male more conspicuously 

 modified, apparently two-jointed, with a long apical claw. This 

 genus very closely approaches Centropages, which latter is its marine 

 prototype. The genus is represented by two species, one of which is 

 circumpolar, the other occurring in China farther south. 



*Not dejcribed by the author. See plates. 



