704 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [4] 



stouter, and less regularly curved. I have not been able to find positive 

 and unvarying distinctions between this form and the preceding, and 

 am disposed to regard it as the barely matured adult, reproducing while 

 yet capable of further structural progress. Its average total length, 

 without setae, is l mm , the thorax measuring ,7 mm and the abdomen .3 mm . 

 The antennae are relatively longer than in the typical form, extending 

 live or six joints beyoud the cephalothorax instead of two or three, as 

 in the other. The inner ramus of the left leg is also relatively longer, 

 reaching to the tip of the outer ramus, while in the typical form it 

 reaches only to the base of the preceding joint. 



Both the above are extremely abuudaut in all the collections made 

 from northern Michigan, and are likewise among the commonest Euto- 

 mostraca of southern Lake Michigan and adjacent waters. The more 

 highly developed variety is relatively commoner in the Great Lakes, and 

 the imperfect form is the ordinary Diaptomus of the smaller lakes and 

 permanent ponds adjacent. The latter, if either, is to be identified with 

 the insufficiently described Diaptomus pallidus of Herrick.* 



Epischura lacustris Forbes. (PI. I, figs. 1-5; PI. n, fig. 7.) 

 Araer. Nat., xvi (1882), p. G48. 



This remarkable species,! the most peculiar of oar fresh-water Cope- 

 poda, distinguished from all others known by the modification of sev- 

 eral abdominal segments in the male as a sexual grasping organ, was 

 common in both Lake Superior and the smaller lake — most abundant 

 in a collection made at night in the harbor at Marquette. 



Among the many hundreds of specimens which I have examined from 

 the Great Lakes and from several of the smaller lakes of Illinois, Michi- 

 gan, and Wisconsin, I have rarely seen an immature form, still more 

 rarely a female without a spermatophore attached, and never one with 

 an egg sac. The spermatophore (occasionally there are two) is fixed to 

 the female abdomen by a large oval mass of cement, which may be so 

 softened by a solution of potash as to- permit the removal of this finger- 

 shaped structure, otherwise easily mistaken for a process of the abdo- 

 men itself. The absence of an external egg mass is one of several 

 features of this genus relating it to Heterocope of the lakes of Europe, 

 which genus is indeed its nearest ally. 



Specimens taken from LakeMichigamme, August 9, were tinged with 

 red or violet, most deeply in the ventral region, as if a much more 

 brilliant color had largely faded. 



The cephalothorax of the male (PI. i, fig. 1) has but three completely 

 distinct segments, the last being united to that preceding, and that bear- 



* 7th Ann. Rep. Geol. and Nat. Hist. Surv. of Minn. (1878), p. 91. 



tTwo additional species of this genus, E. nevadcnsis Lillj. and E. vordenskiceldi 

 Lillj., the former from lakes in the Sierras and the latter from Newfoundland, have 

 lately been published in Revision des Calanides d'Eau Douce, par Jules do Guerue et 

 Jules Richard, pp. 92-96 (Paris, 1889). 



