EEV. A. E. EATON ON RECENT EPHEMEEID^ OR MAYFLIES. 133 



Nymph No. IV.— PL XL. 1-17 (whole figure & detaas). 



Synonymy. ? Heptagenia t pudica {njm^ha.-skm) , ! H3g. Ann. Rep. U. S. Geol. & Geograpli. Survey 

 of the Terr. 1873, part iii. Zool. 582 (1875) [not subimago, p. 581]. 



Nymph-slough. — Mouth-organs and tracheal branchite of a type similar to tliose of 

 Ephemerella ; body stouter, the abdomen in its broadest part wider than the thorax, the 

 dorsum unarmed, the venter convex; antennae inserted about midway between the 

 anterior ocellus and the sides of the face; first joint of the palpus of maxilla i. upwards 

 of twice as long as the second, the terminal joint about f as long as these combined; 

 tracheal branchiae borne by segments 4-7 of the abdomen, but probably absent from 

 segment 1. — Body broadest at about the fifth abdominal segment, narrowed thence 

 in both directions, but nearly as broad in the mesothorax ; abdomen broadly oniscoidal, 

 the pleurae strongly developed in segments 2-9, and produced into slender acuminate 

 recm'ved teeth, w4iich are pilose where the tracheal branchiae do not overlap them ; the 

 penultimate segment the longest, in dorsal view somewhat similar to a mitre with the 

 cleft partly choked seen sideways. Caudal setse of $ mutually subequal in length, and 

 very nearly ^ as long as the body ; median seta plumose ; outer setae ciliated on the 

 inner side near the roots, and plumose distally. Pronotum transverse, quadrangular, 

 rather broader behind than in front, gently arched, slightly compressed on each side, and 

 armed with a short conical tubercle on each side in the middle near the boixler. Le£;s 

 pilose, very similar in their proportions to those of Ephemerella ; femora prolonged at 

 the knee each into a short acute spine ; intermediate coxae each armed above with a 

 short conical tubercle. Head small, transverse, narrower than the pronotum, wider in 

 front than behind, slightly constricted at the junction of the frons and vertex; integument 

 minutely spinulose on the frons, pilose at the sides and in front ; vertex transverse, oculi 

 contiguous in 6 ; frons prominent at the base in the vicinage of the ocelli and antenna», 

 and then broadly flattened out so as to form a transverse and projecting ledge or guard 

 over and in advance of the mouth-parts, which ledge is truncate in front, rounded off 

 at the fore corners (where it is broadest), straight-sided, narrowed posteriorly, and much 

 wider than long. Length of body 15, setae 7 millim. 



Sab. Colorado, mountains and plains (Lieut. W. L. Carpenter ; Mus. Comp. Zool. 

 Cambridge, Mass.). The laminae of the tracheal branchiae of segments 4 & 5 are emar- 

 ginate below the tip on one side ; those of the other segments are entire. The palpi of 

 maxillse ii., formerly described as 2-jointed, have 3 joints ; but the small terminal joint 

 is difficult to trace in tbe cast slough. The sloughs of the hind wings are separate from 

 those of the fore wdngs, and are attached in the usual manner to only the hind border of 

 the metanotum ; their tips attain the base of the second abdominal segment. They were 

 formerly described as being incorporated into the notal hood, in a manner similar to the 

 hind winsis of Bcetisca. 



-'»'- 



Nymph No. V.— PI. XL. 18-20, & LXIV. 3-7 (whole figure & tracheal branchiae). 

 Body moderately stout ; mouth-organs and hinder pairs of tracheal branchiae similar 

 in type of construction to those of Ephemerella ; abdomen in its broadest part wider 



SECOND SERIES. — ZOOLOGY, VOL. III. 18 



