NEUROPTEKA— TEIOHOPTEK A— HYDROPS YOHlDyE. 18 1 



2. POLYCENTROPUS Curtis. 



This is an important group of caddis-flies to the paleontoh^gist, since 

 nearly one-half of the many phryganids described from the Prussian amber 

 belong to it, audit is interesting to find that we have at least one species in 

 our own rocks. The present distribution of the species is mainly in Europe 

 and North America, where they are numerous, with a few recorded from 

 Ceylon. The larvae, according to McLachlan, inhabit shallow, rapid streams, 

 and form, Pictet says, no firm cases until about to change to pupa3. In 

 speaking of the abundance of this group in the amber fauna McLachlan 

 says: "Insects referred to Polycentropus in its broad sense seem to have 

 been very common in the Tertiary period when amber was formed ; their 

 habit of concealing themselves in the crevices of the bark of trees probably 

 caused their entanglement in the resin and subsequent fossilization."^ 



Polycentropus exesus. 



A delicate winged, sparsely clothed species with exceedingly delicate 

 antennae. The body is moderately slight, the head small ; basal joint of 

 antennse very stout, subglobular, the remainder thread-like, reaching back 

 beyond the closed wings, the joints three to four times longer than broad 

 and narrowly ringed with black at the incisures. Legs poorly preserved in 

 miost of the specimens, but only moderately slender, the tarsi rather densely 

 spinous. Wings moderately slender, bi'oadest at the anastomosis, the apex 

 rather broadly rounded, tolerably clear, but with heavily infuscated veins ; 

 the discoidal is much longer than the median cellule, and the second apical 

 cell is longer than the third and fourth, and of about equal length with the 

 fifth ; the anastomosis above the fifth fork lies in a curve subparallel to the 

 apical margin. 



Length of body, 7.6°"° ; of front wing, S™"" ; width of same, 2.6°"° ; 

 length of antennae, 11°"°; of hind tibiae, 4°'°'; of hind tarsi, S.S""". 



Florissant. Nine specimens, Nos. 67, 571, 3143, 7428, 7873, 9549, 

 10501, 12441, 13529. 



' Trichoptera Europ. fauoa, 398. 



