252 REV. A. E. EATON ON RECENT EPHEMERID^ OR MAYFLIES. 



median sinus. Fangs of the mandibles very unequal and of peculiar construction : 

 viewed from beneath (PL LIV. 8 and 9) without compression, the exterior and much the 

 larger fang, which is set obliquely in relation to the stipes, appears falcate, sharply 

 truncate at its outer base, just opposite the very rudimentary interior fang, and serrulate 

 for some distance before the tip along its outer edge : viewed from above under pressure 

 (PL LXV. 6) each fang opens out into a concave expansion ; the exterior becomes acutely 

 subovate triangular, truncate at the inner basal angl , where it joins the crown of the 

 mandible, and displays fine serrulations along both its lateral margins, while its base is 

 pectinate or ciliated and inflexed ; the interior fang [or ? endopodite] partly contained in 

 the concavity of the outer fang, is oblong-cochleariform or like an oblong scoop, slenderly 

 serrulate at its terminal border, finely and densely pectinate along the upturned edge 

 subtended by the concavity of the outer fang, and sparsely ciliate aloug the opposite edge. 

 The hairs comj)Osing the tuft near the inner bases of the fangs appear unilaterally plumose 

 when highly magnified in a favourable light. Lacinia of maxilla i. beset along the edge 

 of the crown with appressed pectinate teeth : proximal joint of the palpus broadly dilated 

 behind : terminal joint stoutly clavate, oblique at the extremity, and densely scahrid 

 externally from near the base to the acute point. Median lobe of the tongue (as in 

 Epeorus) quadrilateral, broader than the paraglossae, which are narrow and dilated in the 

 middle. Eemora marked on the coloured side each with a conspicuous isolated dark 

 spot, in or about the middle, and sometimes clouded with grey between that and the tip. 



NORTH AMERICAN SPECIES. 



Rhithrogbna jejuna (renamed). 



X Baef'ts W/usca, ! Walk., List of Neuropt. Ins. in Brit. Mus. part iii. 568 (1353) ; Hag., Smitlison. 

 Miscell. Coll. (1861) Synop. Neuropt. N. Am. 45. 



Heptagenia fusca, ! Etn., Trans. Eut. Soc. London (1871) 138, pi. vi. 13-13 6 [detail]. 



Imago {dried). — s . Thorax dull rufo-piceous above. Abdomen in segments 2-5 

 translucent burnt-umber brown, with the apical borders of tlie dorsal segments darker. 

 Porceps bistre-brown. Legs bistre-brown ; the femora each with a black longitudinal 

 streak tajjeriug at both ends and commencing at a short distance from the base ; the 

 apical lobe of the fore tibia pitch-black. Wings vitreous, the membrane tinted with very 

 light bistre-grey, scarcely darker or greyish-tinted in the pterostigmatic space ; neuration 

 pitch-brown ; the marginal area of the fore wing contains about 3 cross veinlets before 

 and 19 beyond the bulla ; many of these in the pterostigmatic region divide irregularly 

 and anastomose with one another. 



S . Abdomen bistre-brown, the distal borders of segments 3-8 rather broadly margined 

 with pitch-black. In the marginal area of the fore wing are about 6 ci-oss veinlets 

 before, and 21 beyond the bulla. Length of body 6-7, wing 9-10 mm., in both sexes. 



Hab. St. Martin's Palls, Albany Eiver, Hudson's Bay (Brit. Mus.). The specific 

 name of this species should be rendered " uninteresting". 



