266 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
developed, and the first thought would be that this must be a primi- 
tive synthetic type; in other words, historically the oldest of Cladocera. 
Closer study does not warrant the theory. There is much to indicate 
that, though essentially lynceid, it stands in close connection with the 
higher members of the family and perhaps has more than a superficial 
resemblance to such degraded Lyncodaphnids as Ilyocryptus. All things 
considered, however, our diagram stands with this genus as a 
degraded offshoot of the more typical stem of Lynceide. 
SUB-ORDER GYMNOMERA. 
This group is easily recognized by the almost entire absence of the 
shell, which forms so conspicuous a part in the greater number of the 
Cladocera. Here it serves simply to form a pouch or brood-sac for 
carrying the eggs and embryos. The feet are nearly terete and pre- 
hensile, with but slight indications of branchial appendages. 
FAMILY POLYPHEMIDE. 
Feet five pairs. Antenne with the rami three- or four-jointed. 
GENUS POLYPHEMUS De Geer. 
Head very large, separated by a depression from the compact body; 
shell covering but a part of the dorsal region. Feet all with an inter- 
nal dentate and an external lamellate appendage. Caudal seta upon 
a long process of the post-abdomen. 
* Polyphemus pediculus Linn. 
PuLatTeEs LVIII, Fies. 4-6; LXIX, Fie. 1. 
Monoculus pediculus—Linnzeus, 1746. Gmelin, Linn. Syst. Nat. Fabricius, Ent. Syst., 
etc. Sulzer, Insecten. Manuel, Encyclop. Meth. 
Monoculus pediculus ramosus—De Geer, Mem. pour serv. a |’ Hist. des. Ins. 
Polyphemus oculus—Mueller, Zool. Dan. Prod. et Entomost. Cuvier, Tab, element. 
Latreille, Hist. Nat. Crust., ete. Leach, Edin. Encyc. 
Polyphemus stagnorum— Leach, Dict. Se. Nat. Latreille, Cuv. Reg. An. Demarest, 
Cons. Gen. Crust. 
Polyphemus pediculus—Straus, Mem. Mus. d’Hist., etc. M. Edwards, Hist. Nat. Crust. 
Monoculus polyphemus—Jurine, Hist. Nat. Monoc. 
Cephaloculus stagnorum—Lamarck, Hist. An. Vert. Bosc, Man. d’Hist. Nat. Crust. 
Monoculus oculus—Gmelin, Linn. Syst. Nat. 
Sealicerus pediculus—Koch, Deutsch. Crust. 
Polyphemus pediculus—Baird, Brit. Entom. 
Polyphemus oculus—Lievin, Branch. d. Danz. 
Polyphemus stagnorum—Fischer, Ueber die in d. Umg. von. St. Petersburg vorkom 
Crust. 
