120 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



lum is also more elongate, but this is subject to considerable varia- 

 tion. 



The armature of the feet, structure of antenme and most diagnostic 

 points agree so fully that I hesitate to separate the two forms. In the 

 description of G. diaphanns given in the first edition some of the state- 

 ments apply to C. varicans or an allied form. The form of the recep- 

 taculum figured on Plate E, Fig. 12, of that report may be compared 

 with that of Plate VII, Fig. 3", Crustacea of Alabama, to illustrate 

 the range of variation. 



* Cyclops pbaleratus Koch. 



Plates XVII, Figs. 1-7; XVIII, Figs. 2-2 '>; XIX Fig. 1; XXI, Figs. 6-10. 



Koch '35; Fischer '51 (canthocarpoides); Lilljeborg '53 (canthocarpoides); Claus '57 

 and '63 (canthocarpoides); Lubbock '63 (canthocarpoides); Sars '63; Fric '72 (can- 

 thocarpoides); Poggenpol '74 (lascious); Uljanin '75; Brady '78 and '91; Herrick 

 '82 (adolescens), and '84 and '87; Cragin '83 (perarmatus); Daday '85^; Eichard 

 '91; Schmeil '91 and '92; Turner '92; Marsh '93. 



Body sub cylindrical, thorax little enlarged for the genus, abdomen 

 large and cylindrical. The transition from thorax to abdomen is less 

 sharply marked than usual. Cephalothorax oval, first segment longer 

 than the remainder. Abdomen shorter than thorax, stylets short and 

 profusely spinous. An oblique row of spines passes across the stylet 

 some distance behind the lateral spine, which is very short, and other 

 rows of spines or teeth may ornament the inner aspect or may be 

 absent. The whole inner aspect is also ciliate. The outer apical seta 

 is a ciliate or toothed spine and the inner is shorter and weaker. The 

 outer median seta is nearly as long as the abdomen and is sparsely 

 clothed with sharp teeth. The inner median seta is about half as long 

 and similarly ornamented. The antenna is usually 10 jointed but fre- 

 quently is 11-joiuted, (?) and is much shorter than the first thoracic 

 segment. The swimming feet all have three jointed rami and are 

 strongly armed with closely set short teeth. The armature of the ter- 

 minal joints of the fourth foot is as follows: 



j' ex. 



Outer ramus < ap. 

 (in. 



Egg-sacs appressed, closely filled with many ova. I here append 

 the original description of Cyclops adolescens Herrick (=0. perarmatus 

 Cragin) for comparison with the description of C. affinisas transcribed 

 below, as it contains other data: "Thorax oval, broad, acute ante- 

 riorly; last segment large and separated by a constriction from the 

 anterior ones. The head is beaked below; fiist thoracic segment large 

 and long (0.36 mm.); last thoracic segment wide, united closely with 

 the first abdominal segment, armed with series of teeth. Abdomen 



