PERLODES MICROCEPHALA 71 



quite the exception to meet with other species 

 than the five first named on chalk-streams. 



A vast Order upon which the dry-fly fisher- 

 man occasionally draws is the DIPTERA two- 

 winged flies, bred both on land and in water ; 

 a small Family, the SIALID^:, furnishes the 

 alder (Sialis lutarid], which has become a 

 much-respected trout-fly partly from its pre- 

 sence in immense numbers on the bank, giving 

 rise to the impression that as many must be 

 present on the water ; and partly from the 

 resemblance that the artificial fly bears to 

 many types of TRICHOPTERA or caddis-flies, 

 when fished dry, or to shrimps, minnows, and 

 other aquatic forms of life when wet. 



Family . . 



Genus . . Perlodes (Dictyopteryx) 



Species . . microcephala 



PLATE XIV 



The only large stone-fly at all abundant PERLODES 

 on our chalk-streams is Perlodes microcephala. 

 I have found it in plenty along the banks 

 of the Kennet, hiding during the daytime 

 under the loose bark of trees and in chinks and 

 crannies of fencing bordering the river. 



It is rather smaller than the large stone-fly 

 (Perla maxima and P. cephaloles) of north- 

 country streams, and may be distinguished 

 further by the arrangement of the markings of 

 the head and thorax. The male has short rudi- 



