182 TEET1AEY INSECTS OP NORTH AMEKIOA. 



POLYCENTROPUS (?) EVIRATUS. 

 PI, 13, Fig. 7. 



A single specimen with its reverse is placed here provisionally simply 

 from its general resemblance to species of this group. A crushed body, 

 heavily scaled wings, an antenna, and a fragment of a leg are all that 

 remain. The body is stout and apparently clothed densely. The antenna 

 is rather slender, tapering, about as half as long as the wings, and com- 

 posed of joints of equal length and breadth. The wings are folded some- 

 what, so that their form can not fully be seen, but they are apparently not 

 slender and are very densely scaled, concealing all neuration ; the costal 

 margin is very gently and slightly convex, curving downward to the apex 

 only at the very tip, the apex far above the middle of the wing, and the 

 apical margin oblique, straight, not retreating rapidly. 



Length of body, ll mra ; of front wing, 10.5 mm ; of antennse, 5 mm . 



Florissant. One specimen, Nos. 12239 and 12240. 



3. DEROBROCHUS gen. nov. (drjpos, /3p6%o;). 



A large proportion, both of the specimens and species, of Florissant 

 caddis-flies seems to belong to this new type of Hydropsychidse; which is 

 allied to Polycentropus in many of its features, but is remarkable for the 

 length of the cells and for the apparent want of any fifth apical cell. The 

 median cellule, which is generally longer than the discoidal, is often one- 

 third, or even more than one-third, the length of the wing, and the lower 

 branch of the upper cubitus runs straight or nearly straight to the margin, 

 bending sometimes near the cross- vein which, near the margin, connects it 

 with the vein below. The uppermost apical cell, as in Polycentropus, is 

 small, and in general the affinity of this genus to that is marked ; but the 

 absence of the fifth apical cell is believed to be sufficient ground for generic 

 distinction, as that cell is generally found throughout the family. The 

 cross-vein uniting the upper and lower cubitals is variously situated. 



Table of the species of Derobrochus. 



Base of first apical cell of front wing not, or scarcely, farther from the root of the wing than the base 



of some of the other apical forks. 



First apical cell almost as long as the second; this not greatly longer than the third.. 1. D. abstractus. 

 First apical cell much shorter than the second ; this nearly twice as long as the third. 



First apical coll longer than the fourth '2. D. I:H /</. 



First apical cell shorter than the fourth. 



First apical cell curving upward 4. D. commoratu*. 



First apical cell with no upward curve <J. 1). friijeaceiis. 



