120 TERTIARY INSECTS OF NORTH AMERICA. 



EPHEMERA Linnet 



The species known only in the immature stages may be distinguished 

 as follows : 



Table of the species of Ephemera. 



Outer caudal setae fringed on both sides. Middle seta as long as the outer seta 1 . 



SetEe very much more widely fringed in the middle than toward either end ; dorsal abdominal 



markings consisting of light blotches on a dark ground 1. E. tabifica. 



Setae only a little more widely fringed in the middle than toward the base or tip ; dorsal abdom- 

 inal markings consisting of light lines on a dark ground 3. E. macilenta. 



Outer caudal set:o fringed on the inner side only, and very much more broadly in the middle than 



near the base or tip. Middle seta shorter than the outer setae 2. E. imniobilis. 



Seta? of equal length and naked, or not noticeably fringed. 



Large species. Head less than half the width of thorax; dorsal abdominal markings of light 



lines 4. E. pumicosa. 



Small species. Head considerably more than half as wide as the thorax ; no dorsal abdominal 

 marking 5. -E. interempta. 



1. EPHEMERA TABIFICA. 



Pupa. This species differs somewhat in form from the other larger 

 types, the abdomen being very nearly of equal size throughout and the 

 thorax nearly twice as broad as it, while anteriorly the whole body tapers 

 regularly, as in the succeeding species. The head is rounded quadrate, 

 about half the width of the thorax. The legs are slenderer than in the 

 succeeding species and short, the front pair no longer than the width of the 

 thorax, the hind pair longer, being as long as the head and thorax together. 

 The wing pads are blackish, about three times as long as broad, reniform 

 in shape, the inner margin bent in the middle, and the basal halves of the 

 inner margin of the two wings meeting to form an angle slightly less than 

 a right angle, the apical half tapering to a rounded apex. The abdomen 

 is long and slender, the apical joint more than half as broad as the basal, 

 the dorsal surface blotched with large quadrate patches of lighter color 

 than the ground, sometimes central, sometimes anterior and transverse, 

 divided by a median line. The three caudal setre are slender, less than 

 half as long as the abdomen, equal, very broadly fnnged on either side in 

 the middle. 



Length of body exclusive of setse, 25 mm ; breadth of thorax, 4.5 mm ; 

 of middle of abdomen, 2.6 mm ; length of wing pads, 4.5 mm ; of front legs, 

 4 mm ; of hind legs, 8 mm ; of seta?, 7 mm . 



Florissant. One specimen, No. 13238. 



