29-4 Birge — Notes on Cladocera. 



Ceriodaphnia lacustris, sp. nov. 

 Plate XII, Figs. 6, 7, 8, 9. 



Female. — The head is small, greatly depressed and slightly an - 

 gulated in front of the antennules. The vertex bears numerous 

 small spines at the angle of the reticulations. The fornices are 

 very large, extending out in a broad triangular plate whose 

 apex is blunt and armed with three or four teeth. The valves 

 are ventricose in the posterior ventral portion and the dorsal line 

 is somewhat arched. They are not very strongly reticulated. 

 The posterior spine is well developed and stout. It is occa- 

 sionally divided at the tip into a right and left part, but usu- 

 ally terminates bluntly with 2-4 teeth. The post-abdomen 

 is somewhat like that of C. reticulata, being long and narrow, 

 bearing 6-8 recurved anal teeth, which increase in size to- 

 ward the posterior end of the abdomen. The caudal claws are 

 long, recurved and denticulate. 



The eye is of moderate size and its numerous lenses project 

 far out of the pigment. The macula nigra is small and quad- 

 rangular in shape. 



The antennules are short and rather thick. They are not 

 much longer than the sense-hairs which they bear. The ante- 

 rior sense-hair is placed near the apex of the terminal joint. 

 The antennae are small and slender. 



The fornices in this species seem to exceed in size anything 

 before noted in this genus. The distance between the tips of 

 the fornices nearly equals the greatest breadth of the animal. 

 TThe spine is better developed than is usual in Ceriodaphnia. 

 The reticulation of the valves is more plainly marked than in 

 C. quadrangula, less strong than in G. laticaudata. 



The supra-ocular depression is not deep, while the cervical 

 notch is deep. 



The color is yellowish-transparent. The species is pelagic, 

 although single individuals may be found in the weedy margins 

 of lakes. It has been found at Madison, Minocqua, Tomahawk 

 lake, Twin lakes, and Rhinelander (lake Julia), all in Wiscon- 

 sin, and at G-ogebic lake, Michigan. Length of female, 1-1.3 

 mm. 



