ENTOMOSTRACA OF MINNESOTA. Ill 



In the previous edition it was suggested that this is but an atavistic 

 form of G. pulcliellus = C. strenuus, and although Sehmeil does not 

 accept this suggestion, he adds strong j)robability to it by noticing 

 that the eighth joint of the antennae show indications of subdivision 

 and have the armature requisite to correspond with C. strenuus after such 

 division. Against the suggestion heurges,(l) thatthisformisnotsimply 

 found in scattered individuals but in large groups; (2) that there 

 seems no sufficient reason for such suppression; (3) that the animal is 

 often very large, and we should therefore expect it to attain its full 

 development. To these it must be replied (1) that it is very common 

 for Gopepods of a given stage to be a-ssociated almost to the exclusion 

 of others, thus the net will sometimes bring in from a given locality 

 almost solely half grown Diaptomi where on a previous visit adults 

 preponderated; (2) that we know too little of the biology of these ani- 

 mals to plead our ignorance as a reason for rejecting what is anatom- 

 ically probable; (3) rapid increase in size (unusually rank nutrition) 

 may be just a condition for retardation of development, as it often is 

 in other groups of Crustacea. Questions of this nature demand careful 

 and continuous observation and experiment, and should not be arbi- 

 trarily closed by a priori arguments. 



Respecting G. luhhockii Brady, whether it should be considered an 

 atavistic form of G. strenuus or of G. hicuspidatus is difficult to say. Its 

 brackish habitat speaks strongly in favor of its not being a distinct or 

 permanent species. The short first thoracic segment and antenme 

 incline me to ally it to the latter species. Specimens sent me by Mr. 

 E. A. C/ongdon of Columbia College, from Long Island, seemed iden- 

 tical with G. luhhocMi Brady, and if this form cannot be brought into 

 relation to a 17-jointed species, Brady's earlier name should be 

 revived. It must be observed, however, that the American specimens 

 were within direct influence of the sea. 



* Cyclops serrulatus Fischer. 



Plates XV, Figs. 8-11; XIX, 2-5; XXVI, Fig. 10; XXIX, Figs, 17-19. 



Fischer '51; Lilljeborg '53; Clans '57 and '63; Sars '63; Lubbock '63; Heller '70; Fric 

 '72; Hoek '78; Brady '78 (serrulatus var. montanus, and serrulatus); TJIjanin 

 '75; Herrick '82, and '84 (serrulatus var. elegans, and serrulatus); Eehberg '80 

 (agilis); Cragin '83 (pectinifer); Daday '85^ (agilis); Sostaric '88 (agilis); Thall- 

 witz '90 (agilis); Lande '90 (agilis); Richard '91; Schmeil '91 and '92; Marsh 

 '92; Turner '92. 



The commonest and most abundant species of the Eastern States. 



Cephalothorax oval, compact. Abdomen slender and about three- 

 fourths as long as the thorax, cylindrical, suddenly enlarged before 

 its union with the thorax. Antenate slender, reaching nearly to the 



