384 Heterogenetic Development in Diaptomus. [April, 



Diaptomiis leptofus has not been recognized in the South. 



Fig. 4 of Plate viii in the Naturalist, July, 1882, represents the 

 process or inner branch of fifth foot reversed, probably by pres- 

 sure ; Fig. 6 of the same plate omits one of the setae on the last 

 joint. Now comparing these figures with others, we see less dif- 

 ference than as given. 



Epischura fluviatilis, sp. nov. (Figs. 10-20, Plate v). 



The genus Epischura, which was founded by S. A. Forbes^ 

 upon a species of Copepod, E. lacustris, inhabiting Lake Michigan, 

 is one of the most interesting as well as anomalous of the genera 

 of Calanidse. The typical family likeness is preserved, but there are 

 several peculiarities which have no parallel in Copepoda, if else- 

 where. 



The animal for which the name Epischura fluviatilis is proposed, 

 is undoubtedly extremely near the above, but in several respects 

 disagrees with the points in Forbes' description which he seems 

 to rely upon as of generic importance. It might be assumed that 

 these differences have generic value, and I should be inclined to 

 so regard them except that there seems a possibility that Mr. 

 Forbes has slightly mistaken the homologies of the anomalous 

 organs as indicated below. 



As no generic characters were given, this second species may 



warrant an attempt, as follows : 



Epischura Forbes, 1882. 



Char. gen. — Cephalothorax slender, 5-6-jointed ; abdomen 4-jointed in male. 3- 

 jointed in female; second antenrtce as in Diaptomus; mandibular palp biramose ; 

 swimming feet all biramose; inner ramus i -jointed; left foot of last pair aborted 

 or obsolete, right foot in female slender, last feet of male greatly modified (right?), 

 foot liiramose, inner ramus short, lamellate, i -jointed with claw-like setae, outer 

 branch nearly like female, left foot coalesced with the first two jomts of abdomen, 

 extremity alone free; seta; of caudal stylets three. 



Forbes says of E. laaistris that the female has a process upon 

 the abdomen and in both sexes the latter is curved and deformed. 

 In E. fluviatilis the abdomen of the female appeared normal, 3- 

 jointed, and differs in no way from Diaptomus except as to the 

 number of setse. It is to be remarked that Epischura offers an ex- 

 treme example of the tendency noticed in all Copepods, as well as 

 frequently in higher Crustacea, to diminish or abort the inner 

 branch of biramose organs on either side the median line. 



^S. A. Forbes. On some Entomostraca of Lake Michigan. Am. Naturalist, 

 July, 1882. 



