236 Illinois State Laboratory of Natural History. 



near the inner margin and opposite the outermost of the 

 other setae. 



First pair of antenna 1 shorter than the body, 25-segmented, 

 the hist segment very small. Eight male antenna geniculate 

 between the 18th and 19th segments, each of which is armed 

 with a hyaline lamina. Outer ramus of second pair of 

 antennae seven-segmented* and armed with very long setae. 

 Mandibles produced at the inferior extremity into nine 

 teeth, of which the outer two are longer than the rest, the 

 inner two slender and setiform ; palpus long and narrow, 

 three-segmented, the last two segments very short, outer 

 ramus small, armed with long seta?. First pair of maxillae 

 about as in Diaptomus. Second pair of maxilla; robust, 

 eight-segmented, the last segment produced into long stout 

 claws; margins otherwise sparsely hairy: the falcate apex 

 bare or' armed with very small dense spines. Maxillipeds 

 seven-segmented, much elongated and narrow, directed for- 

 ward, and armed with numerous long seta?. 



All the swimming legs biramose. Both rami of the four 

 anterior pairs of legs three-segmented, the inner shorter than 

 the outer. 



Outer ramus of fifth pair of legs of female three-segmented ; 

 ;i rmed within, on the second segment, with a very strong, 

 curved, hook-like process. Inner ramus as in the other legs. 



Outer ramus of right fifth leg of male two- (sinensis) or 

 indistinctly three- (macrurus) segmented, the second segment 

 produced into a stout hook-like process. Outer ramus of 

 left fifth leg two-segmented, the second segment armed with 

 a slender digitiform process. Inner rami three-segmented, 

 alike, and similar to £hose of the preceding pair (macrurus), 

 or differing from one another {sinensis). Eye single, near 

 the lower margin of the head. 



This genus was established by Dr. Sars in 1802 to receive 



*The parts of the generic description referring to the structure of the second 

 pair of antennae, the mandibles, maxillae, maxillipeds, and the swimming legs are 

 compiled from sars ("62 ami ''.i7i. Nordqvisl ('88), and de Guerneand Richard ('89b . 

 In regard to the second pair of antennae of macrurus the writers mentioned state 

 that the outer ramus is seven-segmented, anil Nordqvisl says further that the suture 

 between the second and third segments is indistinct, and figures the antenna with six 

 segments. Sars ("97) says of grimatdii that the outer ramus is six-segmented and so 

 figures it. After careful examination. I find no difference in the second pair of an- 

 tenna' of macrurus nn<\ grimaldii, the segmentation being equally distinct, each of 

 the four spines between the second and last segments markim; a segment. 



