254 'BULLETIN OF THE UNITED STATES FISH COMMISSION. 



terminal claw sinuate or irregularly curved. The stout seta on the outer margin of 

 the second segment of this ramus is borne at about a quarter the length of the seg- 

 ment from the distal end, and is approximately half as long as the segment to which 

 it is attached. The inner ramus is a little longer than the basal joint of the outer. 

 It is not dilated or otherwise modified, but terminates bluntly, bearing at the tip a 

 covering of long cilia. 



The right antenna of the male is without notable distinctive characters. The 

 antepenultimate segment is as long as the two following taken together; the fourth 

 from the tip bears two long sword-like spines at its margin, both attached to its basal 

 fourth ; the expanded segments are well armed with conical spines, straight and curved, 

 but without hooks. 



Small lakelet near Gardiner, Montana. 



Epischura nevadensis, var. columbiae, u. var. (Plato XLI, Figs. 19-21.) 



It is with pleasure that I report here the occurrence of another form of this inter - 

 esting genus of North American entomostraca, the fourth or fifth thus far discovered. 

 The first species described, E. lacustris, has been found in the Great Lakes, in the smaller 

 lakes of Wisconsin and Minnesota, and at Portland, Oregon; the second, E.fluviatilis 

 Herrick, has been seen only by the original describer of the species, by whom it is 

 said to occur in Mulberry Creek, (Jushinan County, Alabama.* Epischura norden- 

 sTtioeldii Lillj., is from Newfoundland, and E. nevadensis from lakes Echo and Tahoe, 

 the former in California, the latter partly in that State and partly in Nevada. The 

 present form occurs in Swan and Flathead lakes, in northwestern Montana, where it 

 was the most abundant copepod in the open water. 



The absence of all representatives of this genus from the lakes of Yellowstone 

 Park, evidently adapted to them, hints strongly at a limit of altitude to their distribu- 

 tion. The highest locality from which any species has been reported is Lake Tahoe, 

 said to be 0,250 feet above the sea; while the lowest lake of suitable size in Yellow- 

 stone Park from which our collections were made was 1,200 feet higher than this. 

 This topographical difference does not measure the biological difference, however, as 

 the lower location is also more than five degrees south of the Yellowstone lakes. 



Disregarding the doubtful fluviatilis, the species of Epischura are, so far as known, 

 of north temperate range in North America. The form least modified, both in abdomen 

 and fifth legs, is the Newfoundland species, nordenskiceldii, and the most modified in 

 both is nevadensis, lacustris standing intermediate. The new form, again, is interme- 

 diate between lucmtris and nevadcmix proper and may be roughly characterized as 

 uniting the characters of the fifth legs of the male and female and the caudal set* of 

 nevadensis with those of the abdomen of the male of lacustris. 



* Herrick's species hardly seems to belong to this geuus. Tho abdominal processes are described 

 as projecting from the left side of the abdomen, and consequently can not be homologized with those 

 of E. lacustris. all of which are developed from the right, and the fifth foot of the male is scarcely 

 c apable of close comparison with the corresponding appendages of undoubted Epischura. The differ- 

 ence reported in the position of the hinge in the antenna) of the male also points to a deep-seated and 

 fundamental distinction, not easy to reconcile, it must be admitted, with the agreement in fluriatilis 

 and laciistrii with respect to the inner ramus of the swimming legs, the fifth legs of the female, and 

 the caudal setae. 



