188 TERTIARY INSECTS OF NORTH AMERICA. 



Length of body, 9°"" ; of front wing, e"™ ; breadth of same, 2.2""° ; 

 length of antennae, 21°"". 



Florissant. Sixteen specimens, Nos. 1655, 3638, 3702, 6039, 7030, 

 7149, 7990, 8013 and 10341, 8065, 8325, 8392, 8857, 9578, 10016, 10239, 

 12014. 



6. MESOBROCHUS gen. nov. {nioo?, ^po^oi). 



This is a peculiar group, not only for the limited number of apical cells, 

 the first as well as the fifth being absent, but also for the great and nearly 

 equal length of all the other apical cells and the distance of the anastomosis 

 from the apical margin ; indeed, nearly or quite a third of the wing at the 

 apex is filled only with longitudinal and parallel veins, as in some Lepto- 

 ceridse. The median cell, on the contrary, is not very long, as it is in 

 nearly all the other genera we have here considered ; the discoidal cell 

 appears to be open, an anomalous peculiarity for one of the Hydropsychidse. 



Table of the species of Mesoirochua. 



Fore wings nearly four times as long as broad 1. if. lethwus. 



Fore wings scarcely more than three times as long as broad 2. M. imbecillus. 



1. Mesobrochus lethwus. 

 PI. 15, Fig. 11. 



A small slender species. Body slender, moderately clothed with scales. 

 Antennse with basal joint very large, as long as the head, the rest slender 

 and cylindrical, tapering sensibly to the tip, as long as the body (without 

 the wings). Legs very slender. Wings very long and slender, the rounded 

 apex in the middle line and the margins curving equally to it above and 

 below ; second apical cell nearly half as long as the wing, third and fourth 

 stopping abruptly at the anastomosis, which falls just beneath the tip of 

 the subcostal nervure ; the discoidal cell is open and the median not very 

 long, reaching as far toward the base as to bring the base of the second 

 apical cell over its center ; the neuration as given in the plate is wrong. 



Length of body, 6°"°; of front wing, 7"°'; width of same, 1.85°"°; 

 length of antennse, 6"°. 



Florissant. Fourteen specimens, Nos. 544, 1665, 2268, 2520, 2566, 

 4584, 6884, 7792, 7898, 10720, 10899, 11132, 12015 and 12789, 13540. 



