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 degrsided Lyncodaphnids as Iluocri/ptus. All things 

 considered, however, our diagram stands with this genus as a 

 degraded offshoot of the more typical stem of Lynceidce. 



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 POLYPHEMID^. 



Feet five pairs. Antennae 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. 



* Polyplieiims pediculus Linn. 

 Plates LVIII, Figs. 4-6; LXIX, Fig. 1. 



Monoculus pediculus— lAwa^ns, 1746. Gmelin, Linn. Syst. Nat. Fabricius, Ent. Syst.^ 



etc. Sulzer, Insecten. Manuel, Encyclop. Meth. 

 Monoculus pediculus ramosus — De Geer, Mem. pour serv. a I'Hist. des. Ins. 

 Polyphemus oculus — Mueller, Zool. Dan. Prod, et Entomost. Cuvier, Tab, element. 



Latreille, Hist. Nat. Crust., etc. Leach, Edin. Encyc. 

 Polyphemus stagnorum — Leach, Diet. Sc. Nat. Latreille, Cuv. Reg. An. Demarest, 



Cons. Gen. Crust. 

 Polyphemus pediculus— ^iraxxs, 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. 

 Sealieerus 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. 



