224 EEV. A. E. EATOX O^; EECENT EPHEMERID.E OE MAYFLIES. 



subimago the median seta is about \ and the outer setae nearly f as long as the body. 

 Oculi of cJ remote above, oval and very prominent. Vertex of 2 head about as long as 

 broad, slightly wider in front than behind ; the occipital border raised suddenly above 

 the level of the posterior orbits of the oculi. Median ocellus of ? much smaller than 

 the others, isolated in a broad descending groove in front of and below the anterior edge 

 of the upper surface of the head. Pronotum of 2 rather broadly reflexed upon the 

 mesopleurse ; its posterior border (viewed from above) arched, with a very shallow median 

 recess, which is oot noticeable when viewed from in front. 



Nymph. — Abdominal tracheal branchiae recumbent upon the dorsum, borne by segments 

 1-6, diversiform and single, each inserted in a notch in the hind margin of the segment 

 adjacent to the plem-a ; the foremost oblique, and somewhat resembling a truncate tri- 

 angle with obtusely rounded angles, placed with the longest side inwards ; the remaining 

 five are formed each of a somewhat broadly obovate or oval pergamentose lamina with a 

 lai'ge roundly expanded foliated lobe produced from its inner edge [defective in fig. 18]^ 

 the margins of which are irregularly erosc and incised. The tracheation of the lamina 

 gives it a curiously marbled appearance. Antennae shorter than the head, about 12-jointed 

 in adolescence. Mandibular lobes strong and fang-like ; the endopodite well developed ; 

 stipes well developed, circumscribed distally by a shallow constriction. Palpus of 

 maxilla i. a little longer than the lacinia ; the third joint gradually tapering, pungent, 

 about as long as the second and little shorter than the first, but not quite as stout as 

 either of them ; lacinia somewhat lanceolate, with very few hairs on the oblique crown 

 close to the point, and with short eiliae mingled with a few slender curved spines on the 

 inner edge preceded by a few A'ery short hairs nearer the stipes. Laciniae of maxillae ii. 

 falcate, nearly of the same breadth as the narrowly ovate-lanceolate lobes of the labium ; 

 first joint of the palpus stout ; second joint less stout and slightly curved, very little 

 enlarged and almost squarely truncate distally, about as long as the first joint ; third joint 

 about half as long as the second, less stout, and somewhat elongate-oval. Median lobe 

 of the tongue subquadrangular, with the distal corners rounded, longer than broad and 

 slightly retuse, subequal in length to the paraglossse, of which the terminal margins 

 with that of the median lobe constitute together an arcuate curve ; paraglossse dilated 

 distally very moderately. Hind leg a little longer than the fore leg ; tarsus (claw 

 excluded) nearly 1^ as long as the tibia. Abdomen carinate above longitudinally in the 

 middle ; the carination in segments 2-9 produced into short jjoints, each i^rojecting a 

 little over the base of the next segment ; pleura3 in segments 1-9 oniscoidally dilated, 

 forming recurved acuminate serratures. Median seta plumose, the others ciliate inside, 

 each in its distal f ; outer setae about ^ as long as the body. 



Type. O. Wakefiekli, M"Lach. 



Distribution. New Zealand, 



Etymology, oviokoc and -yaarhp, in reference to the lateral serratures of the abdomen. 



Oniscigaster Wakepieldi, M'^Lach. Plate XXI. 36 (wings, legs, <S head, and 

 forceps). 

 Oniscigaster Wakefiekli, M<=Lach., Ent. Mo. Mag. x. 108-9, woodcut (1873, Oct.) ; id., Re^j. Brit. Ass. 



