THE PERLIN.E AND PSOCIN^E. 357 



both North American genera, and are of conspicuous 

 size compared with the rest of the sub-family ; all that 

 are yet known exceeding an inch in dimensions. The 

 former is distinguished for its pectinated antennae ; and 

 one species of the latter, the C. cornuta, has, in the 

 male, largely developed mandibles, whence it has de- 

 rived its specific name. 



(314.) The PerlincR are our next sub- family. These 

 insects possess four narrow naked wings, of which the 

 inferior, in repose, are folded ; the nervures are wider 

 apart than in the majority of the preceding sub- 

 families ; they are almost always obscurely coloured : 

 the insects are of a depressed form, with a large qua- 

 drate head. They fly rarely, and are very inert, allow- 

 ing themselves to be readily captured. Their larvae 

 inhabit the water, where they move by the rowing of 

 their legs ; and they feed upon other small insects : they 

 are more than a year undergoing their changes ; and 

 when they have attained their maturity, they creep up 

 the stem of some water plant, and there quietly await 

 the bursting of their skin, which speedily takes place 

 down the centre of the head and thorax ; and the perfect 

 insect then creeps forth, and flies off as soon as its 

 wings are thoroughly expanded. It is remarkable, that 

 the males are incapable of flight, owing to the frequent 

 shortness of their wings ; thus reversing what is usually 

 the case in insects, of the females being the least pro- 

 vided with these organs, when such a sexual disparity 

 exists. Nemura, Perla, and Eusthenia are the chief 

 genera. The last is a native of New Holland. 



(3 1 5.) Our next, and the last sub- family, the Psocince, 

 is of equally limited extent. They are minute insects : 

 when winged, the wings are unequal in size, the an- 

 terior being considerably the largest, and they are loosely 

 covered with nervures. The typical genus, Psocus, 

 occurs about the stems of trees and on palings, and is 

 said to feed upon lichens. It is contiguous to these 

 insects that the genus Atropos is placed, and which con- 

 tains the so celebrated book-louse, famous for its reputed 



A A 3 



