60 TWELFTH ANNUAL REPORT. 



We now come to a group of related species which are most dif- 

 ficult to circumscribe on account of their extreme variability. Ac- 

 cording to the view of Lutz they would all fall into the old D. 

 hyalina of Leydig. More probably, however, some of these forms 

 are of nearly or quite specific value. 



Sp. lO. Daplinia liyaliiia, Leydig? 



(Plate L, Figs. 3, 5.) 

 Daphnia longispina, Herrick. 



I have elsewhere given a brief account of the post-embryonic de- 

 velopment of a species which agrees best with Leydig's figures of 

 D. hyalina. 



The lower outline of the head is nearly straight, the eye being 

 always approximated toward it. In young specimens the head is 

 sharp in front and crested. The lower margin of the head appears 

 very long and the beak turns backward. The spine is very long in 

 young forms but is short in old females. The male resembles very 

 much the young female. The post-abdomen is narrowed toward 

 the end, the terminal claws are smooth, the anal teeth few and the 

 abdominal processes united. Our specimens are from Paducah, Ky., 

 south of the Ohio river. 



I do not know how to distinguish D. Icevis^ Birge, from D. hyalina, 

 save that the abdominal processes are said to be distinct. Both 

 forms were observed in the above mentioned gathering. If, how- 

 ever, Birge's figures are characteristic, he had a difi'erent variety 

 before him from ours; it seems somewhat like D. galeata. 



D, pellucida^ P. E. Mueller, differs from D. hj^alina in the pre- 

 sence of a series of small teeth on the caudal claws, and a more 

 strongly curved beak. 



It is just now brought to my attention that P. E. Mueller, in a 

 late work, identifies D. pellucida with D. hyalina, though he still 

 holds D. galeata distinct. 



Daphnia g'aleata, Sars. 



( Plate T. Figs. 7, 8.) 



According to P. E. Mueller, this species differs from D. pellucida 

 in the absence of teeth on the caudal claw, and, in one variety, by 

 the acuminate head, which seems the only form for which the name 

 is distinctive. Kurz found only the var. frons rotundata. Accord- 

 ing to Forbes, both varieties, the first of which he identifies with 

 D. pellucida, occur in lake Michigan. 



