EEY. A. E. EATON ON EECENT EPHEMEEID.E OR MAYFLIES. 265 



Hab. Dakota, 1872 ; 20 examples captured by Mr. Coues (Mus. Comp. Zool. Cambridge, 

 Mass.) communicated by Dr. Hagen. 



HEPTAGENIA, Walsh, 1863; restricted, Etn. 1881. 



Illustrations. Adult (details), Pis. XXIII. & XXIV. 45 ; see also [anatom.] citations 

 of Palmen (1884) under II. Jlavipennis and sulplinrea; (whole figures) see citations, 

 under the same species of Sulzer (1776), Panzer (1805), and Pictet (1813-5). Nijmph, 

 PL LX. 



Adult. — First joint of the hind tarsus shorter than the second, which is either equal 

 to or a little longer than tlie third joint ; the corresponding joints of the intermediate 

 tarsus of like proportions ; first joint of the 6 fore tarsus much shorter than the second, 

 and this equal or subequal in length to the thu'd joint ; first joint of the S fore tarsus 

 much shorter tlian the second, which slightly exceeds the third in length ; ungues each 

 imlike the other. Penis-lobes somewhat explanate, oblong, and svibtruncate at their 

 divergent extremities. — Fore leg of 6 about 1^ the length of the body ; tarsus about 

 If as long as the tibia, Avhicli is very little longer than the femur ; the tarsal joints in 

 the order of their shortening rank 2 equal to 3, 4, 5, 1, and the first is about j as long as 

 the second joint. Fore leg of ? about equal in length to the body; tarsus about f as 

 long as the tibia, which is about y| as long as tlie femur ; the tarsal joints in the order 

 of their shortening rank 2, 3, 5, 4, 1, and the first is J-| as long as the second joint. 

 Hind tarsus of d about | as long as the tibia, which is less thaji | as long as the femur; 

 its joints in the order of their shortening rank in d 5, 2 equal to 3, 1, 4, in $ 5, 2, 3, 1, 4. 

 Ungues each unlike the other in every tarsus. Hind wings of ordinary form ; the axillar 

 region narrow. In the dried ? abdomen tJie relative lengths of the dorsal segments 

 2-10 may be formulated thus: — 5, 7, 8, 8, 10, 10, 8, 6, 7 ; ventral lobe of the ninth 

 segment obtusely rounded or refuse. Forceps-basis of 6 seldom truncate behind, usually 

 slightly prominent between the insertions of the limbs, and refuse in the middle. Penis 

 lobes rather broad, flattened beneath, subtruncate at the tips, and curved outwards to a 

 moderate extent divergently ; stimuli well developed, adjacent to the median line. Outer 

 caudal sette of 6 l^-^^ (but usually twice) tlie length of the body ; those of $ l4-2i its 

 length. Vertex of ? head transverse ; tlie edge of the occiput, transverse in the midst, 

 ascends at the posterior orbits of the oculi usually only in a slight degree ; median ocellus 

 prominent, contiguous with the anterior margin of the upper surface of the head. 

 Pronotum of ? subcordately excised behind ; the reflexed lateral lobes only slightly 

 rounded posteriorly. 



Subhnago. — AVings tinted with yellowish, very rarely with greyish ; neuration opaque, 

 the cross veinlets acquiring a black tint and narrow dark grey borders, the membrane 



ikewise becoming transversely striped in the disk, and the terminal margins bordered 



^ith greyish, shortly before the final moult. 

 Nymph. — Abdominal tracheal branchiae spreading at the sides ; branchial fibrils 



'ascicled and about as long as the narrowly lanceolate lamina?, of which the fifth is the 



ongest, the others shortening successively in a slight degree in both directions therefrom ; 



>ranchial trachese indistinct in the laminae after death, through the absence of pigment. 



SECOND SERIES. — ZOOLOGY, VOL. III. 36 



