58 TWELFTH ANNUAL EEPOET. 



down the back. In young females and in males the slight angle 

 is replaced by a strong knife-like projection which extends into 

 from 1 to 4 sharp teeth, the anterior tooth being directed forward. 

 The males, in particular, have this feature emphasized. D. long- 

 ispina has a somewhat similar projection but the more nearly re- 

 lated forms seem not to show this peculiarity. The beak is slightly 

 curved and the lower margin of the head is slightly sinuate. The 

 shell has the usual square reticulations and is usually very trans- 

 parent but in peaty waters becomes brownish. The size is smalt 

 but variable; 1.8 mm. is a common measurement. The post-abdo- 

 men is narrow, the claws are armed with four or more teeth and a 

 series of lateral bristles. The anal spines are eleven or more in 

 full grown females and decrease only moderately upward. The 

 processes of the abdomen are distinct. The males are smaller and 

 strongly carinated above and of the same form as young females 

 The antennules are rather long, with a short lateral and a long 

 terminal flagellura, which latter is more than twice the length of 

 sensory setas which are partially lateral. The first foot has a strong 

 claw and a longflagellum, while the second feet have a small spiny 

 hook. There is a single abdominal process which is not hairy as. 

 in D. pulex. 



Sp. 6. Daplinia carinata, Sars. 



Very similar to the last but, according to Sars, the claw has no 

 well marked teeth, a short flagellum on the male antenna, aud the 

 abdominal processes are united at the base (which may indeed be 

 sometimes the case in the above.) 



D. cavifrons, Sars, has a prominence on the forehead and the lower 

 margin of the head is strongly concave, otherwise hardly destin- 

 guishable save by the absence of the keel above. 



Sp. 7. Daphnia longispina, Mueller. 

 D. longispina, O. ¥. Mueller. Baird, Letdig, Sars, P. E. Mueller, Kurz. VVeis- 



MANN, etc, 



Oval, elongate; head large, rounded in front, lower margin some- 

 what concave; rostrum long. Spine very long, springing from the 

 middle of the posterior margin. Post-abdomen attenuated toward 

 the end. Terminal claws smooth or simply cilate, spines few. 

 The abdominal processes are united at the base a very little, Flag- 

 ellum of the male antennule hardly longer than the sensory sette. 

 The young have three teeth above as in D. minnehaha. There is 



