rACKAED.] PHYLLOPODS OF NORTH AMERICA. 355 



three hundred miles west of the Missouri River, the Smoky Hill Elver 

 is twelve miles south. The 'divide' between it and Big Creek, one of 

 its tributaries (upon which Ellis is situated), is about one-third of the 

 distance, or four miles. Six miles north is a tributary of tbe Saline 

 Eiver, with a "divide" about midway between it and Big Creek. From 

 these "divides," at varied intervals, are ravines, those upon the north 

 side often deep enough to be called canons, and in some of wliich are 

 small springs, sufficient to maintain pools containing fishes (and Awipbi- 

 pods). The ravines from the south of these 'divides' are more gentle 

 or less abrupt, aud though, upon heavy rains, torrents of 8, 10, or more 

 feet of depth, rush down them, they are ordinarily dry pools of water 

 remaining only two or three weeks at the angles where are blutt' banks, 

 or in other excavated places. In such pools, well up the ravines be- 

 yond where fishes from the creek run up during the flood, these Crusta- 

 ceans are found. They are not found in ' buffalo wallows,' or in any 

 upland pools. Under the circumstances of this year or last only three 

 or four weeks of life can they have. Millions of them perish by the 

 drying up of the pools in July. A less number hatch out after the fall 

 rains, and they can have hardly more than a month to live.' 



II.— THE GEOLOGICAL SUCCESSlO^sT OF THE PHYLLOPODA. 



FOSSIL FORMS. 



Up to this date but four species of fossil Phyllopoda are known from 

 North America; these are: 



Estlieria pulex Clarke;* from tbe base of the Hamilton shale in New 

 York. 



Estlieria ovata T. R. Jones; from the Triassic beds of North Carolina, 

 Yirginia, and Pennsylvania. 



Estlieria dawsoni Packard; from the Quaternary Clays of Canada. 



Leaia leidyi, T. R. Jones; from the Lower Carboniferous of Pennsyl- 

 vania. 



We reproduce the descriptions of the forms described by Prof. T. E. 

 Jones from his monograph of the fossil Estherise. London Palseontologi- 

 cal Society, 1862. 



^ Estheria pulex Clarke, Amer. Journ. Sc. June, 1882, 476. 



" In examining some fragments of soft, olive-colored shale from near the base of the 

 Hamilton proper, in Miles' Gully, Hopewell, Ontario County [N. Y.J, I have detected 

 the above representative of this extremely interesting genus. The little carapaces are 

 never more than f """ in width and ^™'^ in length, and may he described as having 

 the ventral margin nearly semi- circular, the heak central or very slightly anterior, 

 hinge line sloping laterally. The surface is marked by six, or in the largest seven, 

 concentric ridges, which are very broad, with narrow intervening furrows. There ap- 

 pears to be no more elaborate sculpturing of the carapaces than Jones has figured for 

 his species, E. membranacea, -which is the simplest of any as yet noticed. 



"It is interesting to notice that this Estlieria, the first ever found below the Trias 

 in America, and nowhere at so low a horizon as this, resembles in its subcentral beak, 

 its outline and surface markings, this species just referred to, E. membranacea Jones, 

 from the Old Red of Caithness, while all others figured by that author (Mon. Esth. 

 Palseontogr. Society, vol. xviii) all from higher horizons, have the beak anterior and 

 the outline of the carapace more nearly subtrigonal." 



This is a very remarkable species of Estheria, and may yet be found to represent an 

 undescribed genus. It differs from any species of the genus figured by Jones, includ- 

 ing E. membranacea, in wanting a straight hinge-margin. Its small size, few lines of 

 growth, and lack of a hinge-margin, indicate that it is very young, and for that reason 

 may yet prove to be a true Estheria. 



