North American Centropagidce. 235 



makes a remark in regard to the "steady movement in the 

 water," and this is all, to my knowledge, that has been said 

 about the habits of Osphranticum. The following statements, 

 gathered from observation of a number of specimens kept 

 for some time in a large flat dish may therefore be of interest. 

 Their movements in the water are very different from the 

 short jerky springs of ( 'yclops, and they differ also from those 

 of Diaptomus in that they are more regular. The motions 

 of these three genera might perhaps be expressed by tele- 

 graphic symbols as follows : Cyclops, - -; Diapto- 

 mus, - -; and Osphranticum,- — 

 — . Osphranticum swims equally well on the 



dorsal or ventral surface, seeming, however, to prefer the 

 former position. As in Diaptomus, the anterior end is ele- 

 vated in swimming, and the antennae are actively employed. 

 Sometimes it will turn backward somersaults, going over and 

 over in the water, but I have seen this done only when indi- 

 viduals were swimming on the back. When startled they 

 would dart to the bottom, hide for an instant under a bit of 

 debris, and then make another dash, repeating the perform- 

 ance until they deemed themselves out of danger. 



Since 0. labronectum is the only species known, no key 

 will be required. 



L.IMNOCALANUS G. 0. SaRS. 



Limnocalamis, Sars, '62, p. 226. 

 Centropages, cle Guerne, '86, pp. 276-2S5. 



Body long and narrow, the front armed with two book-like 

 processes. Cephalothorax widest at the middle, composed 

 of six well-defined segments ; last thoracic segment not pro- 

 duced laterally but slightly projecting posteriorly and armed 

 on each side with a minute blunt spine. Abdomen slender; 

 in the female composed (furca included) of four (macrurus) 

 or five (sinensis) segments. Furcal rami very long, hairy on 

 the inner margin ; armed with five stout plumose setae (the 

 second from within the longest), and one slender seta (plu- 

 mose in sinensis), shorter than the rest, on the dorsal surface, 



