North American Centropatjidce. 237 



a fresh-water centropagid closely resembling the marine 

 genus Calanus, and until 1889 L. nun-rums was the only rep- 

 resentative known. In that year Poppe described (de Guerne 

 et Richard, '891)) a new species, L. sinensis, from China. 

 The latter, so far as now known, is a purely fresh- water form, 

 and L. macrurus was at first so regarded, but in Asiatic and 

 European countries it has been found to occur in both fresh 

 and salt water, — in America it has as yet been found only in 

 fresh water, — and further search may show that L, sinensis, 

 too, is common to both. L. macrurus is the only American 

 representative of the genus, but it was deemed best to in- 

 clude sinensis in this paper, thus making the revision of the 

 genera treated complete. 



As already stated, the genus is represented by only two 

 species, macrurus and sinensis. The former is common to 

 America, Europe, and Asia, having been found in the river 

 J ana (in East Siberia), in the Caspian Sea, in the Arctic 

 Ocean, in the lakes of northern Norway, Sweden, and Fin- 

 land, and in the deeper northern lakes of North America; 

 the latter, sinensis, has been found only in eastern China. 



Marsh, in his "Limnetic Crustacea of Green Lake" ('97), 

 records some observations on the habits of Limno calanus, 

 and states that it is repelled by bright light and high tempera- 

 tures, and hence performs diurnal migrations which are more 

 pronounced in cold weather. It seems to have two periods 

 of maximum occurrence, May and November, but is found at 

 all times, although never very abundantly. In March and 

 April most of the individuals are immature. 



To my knowledge Limno calanus has never been found with 

 an egg-sac, differing in this respect from Ospliraniicum and 

 Diaptomus but agreeing with Epischura. The spermatophore, 

 a slender tubular structure, adheres to the female for a con- 

 siderable time after attachment. 



From a practical and economic standpoint Limnocalanus 

 is of importance as contributing to the first food of ( '<>r<';i<>nns 

 clupeiformis (Forbes '83a), of Labidesthes sicculus*, and 

 probably of other lake fishes. 



*See Forbes "On the Food Relations of Fresh-water Fishes: a Summary and Dis- 

 cussion." Bull. 111. State Lab. Nat. Hist., Vol. II., Art. VIII.. ]>. 532. 1885. 



