1883.] Heterogenetic Development in Diaptomus. 499 



HETEROGENETIC DEVELOPMENT IN DIAPTOMUS. 



BY C. L. HERRICK. 



( Continued from page 38 g,) 



Cyclops ingens Herrick {Cyclopidce of Minn., p. 228, Plate iv. Figs. 1-8). 



Found in pools near Tuscaloosa, Ala., with Daphnia pulex and Simocephalus 

 daphnoides. The post-imago is somewhat over Jg- in. long, i. e., not quite as long as 

 C' gigas according to Brady, which is very little different. Our form has longer sty- 

 lets and shorter antennae in the ordinary stage, but the mature or post-imago has 

 shorter stylets. In the last stage prior to maturity the stylets are just as figured by 

 Brady for this stage. It is worthy of remark that C. kaufmanni Uljanin, which is 

 certainly founded upon a prematurely gravid larva (feet being 2-jointed and antennae 

 undifferentiated) corresponds perfectly with larvae of C. ingens. 



Brady himself considers C. helleri the same species, and we 

 have here apparently an older stage with fully developed feet but 

 not yet provided \\;ith mature antennae. 



A variety of C. ingens is found in cold springs at Tuscaloosa 

 and elsewhere in Alabama, much less in size and with the propor- 

 tions of the European C. gigcis. 



The large examples in shallow " prairie pools " were masked 

 by dense algas coating. The form of the fifth foot and stylets dis- 

 tinguishes the above from other members of the genus, and one 

 is tempted to regard these forms as varieties of C. gigas simply. 

 C. parous (Cyclop. Minn., p. 229) might be considered a var. of C. 

 ingens. 



Cyclops pectinatus, sp. nov.. (Plate vii, Figs. 25-28). 



Related to C, navus, from which it is chiefly distinguished by a semicircular series 

 of small spines at the base of the greatly elongated caudal stylets. In the post-imago 

 the stylets are nearly half as long as the abdomen ; the antennae ^"each nearly to the 

 base of the third segment. In the ordinary adult the stylets are less elongate. In 

 all forms the lateral setae are one-third frorii the end and the outer and inner ter- 

 minal seta; are short spines ; the fifth foot is as in Navus and the operculum valves 

 is a little different. Most characteristic, however, is a circlet of small spines one- 

 fourth from the base of the stylets. Length over y^^- in, 



Cyclops tenuissimus, sp. nov. (Figs. 24-25, Plate v; Figs. 20-21, Plate vi). 



Section with i^-jointed antenna:. 

 Extremely elongated; antennce reaching a little beyond the first thoracic segment, 

 short jointed, formula — C/ o — ^ t/_ cJool/uUl/ i^ ^ ^ ^^^ terminal joint rather 

 short, armed with three teeth near the extremity; antennules rather long, last two 

 joints slender; fifth foot 2-jointed, second joint with two nearly equal setae; cauda 

 stylet, as in C. tenuicornis ; opening of spermathaeca elongated. 



This Species is the most slender Cyclops known to me, and 

 may be recognized by the toothed terminal joint of the antennae, 

 a character otherwise confined to C tenuicornis, "coronatus stage.'* 



VOL. XVII. ^NO. v. 35 



