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



The points of difference consist in the fact that the antenncT. are 

 shorter than European viridis, reaching only to the second instead of 

 to the third thoracic segment, and that the armature of fourth feet are 

 very unlike the figures and descriptions of European authors, Brady 

 is the only author who figures these parts, and these figures are evi- 

 dently careless, for the antennae on the same plate have a supernu- 

 merary joint. We have examined a number of specimens of this spe- 

 cies from distant parts of the United States, and find, with Marsh, the 

 armature constant or but slightly variable. The proportions of the 

 apical spines of the inner ramus of the fourth foot are the reverse of 

 those given in his figure. The size varies remarkably, passing into 

 the large variety. 1.4 mm. is an an average measurement exclusive 

 of settle. 



Var. b. * Cyclops ing-ens Herrick. 



Plate XXV, Figs. 1-8. 



This is the largest form yet encountered in America and is rarely 

 seen. It is a simple exaggeration of the last, there being no obvious 

 distinctions except the size. It is occasionally over 4.0 mm. long in- 

 cluding the sette or about 3.0 mm. excluding them. 



It may be noticed that the males of this group have a well devel- 

 oped sixth foot. The antennae are strongly modified and amply spined, 

 as shown in the figure. A series of hyaline plates near the joint are 

 well developed. 



* Cyclops vernalls Fischer. (Fide Schmeil.) 



Fischer '53; Sars'63(C. lucidnlus); Claus'6.3(C. elongatus); Heller '70 (C. elongatus); 

 Eehberg '80^ (C. elongatus and C. lucidulus); Cragin '83 (C. elongatus); Herrick 

 '84 (C. elongatus and lucidulus); Daday '85^ (C. lucidulus); Sostaric '88 (C. luci- 

 dulus); Schmeil '91 (C. elongatus) and '92; Richard '91; Brady '91 (C. elongatus). 



We cannot, of course, enter the perplexing synonomy which has 

 been very carefully studied by Schmeil, and we hope that it may now 

 be considered settled. The not quite unexpected discovery that a 

 ITjointed species may, under certain conditions, become 18-jointed 

 rests on the same kind of evidence which Schmeil rejects in respect to 

 our own statements in the case of other species, and offers a certain 

 probability in favor of the frequent occurrence of imperfectly mature 

 but oviparous females, which he rejects without making the necesary 

 investigation by which he might easily have convinced himself of its 

 reality. However, we are fain to accept the evidence that C. elongatus 

 Glaus is but a "post imago" of C. lucidulus Sars. Still it is not to be 

 forgotten that other species may sporadically develop 18 jointed an- 

 tennae and then might lay claim to be considered C. elonr/atus. 



