THE CANADIAN ENTOMOLOGIST 171 



slightly transverse; 9th to 11th forming a loose club. Head and 

 clypeus simple in the male, in which sex there is a small setigerous 

 fovea near the base of the first \entral segment. 

 Sphindocis denticollis, n. sp. 



Rufotestaceous, strongly shining. prothorax and elytra coarsely, 

 closely, uniformly punctate; head similarly but not quite so coarsely 

 so. Prothorax one-third wider than long, sides parallel and broadly 

 arcuate, margins narrowly, abruptly reflexed and quadriden- 

 ticulate. Elytra scarcely wider than the prothorax, slightly more 

 than twice as long as wide, sides parallel to apical two-fifths, apex 

 evenly rounded. Beneath coarsely, closely punctate anteriorly, 

 abdomen except the basal segment finely and sparsely so. Length 

 3.75 mm.; width 1.25 mm. 



California (Alameda Co.). A single male. If we exclude the 

 Rhipidandrinie this is the largest Ciside known to me. In its 

 size and denticulate thorax it somewhat suggests Odontosphindus. 

 The surface, as in Orthocis, is not perfectly glabrous, each 

 puncture bearing a very minute hair. 



SEASONAL IRREGULARITIES IN THE 

 OCCURRENCE OF DRAGONFLIES. 



BY E. M. WALKER, TORONTO. 



The exact composition of the dragonfly fauna of a given 

 locality is subject to frequent change. The effects of erosion on 

 the beds, of streams, the deposition of sediment and the accumu- 

 lation of organic debris in lakes and ponds are constantly produc- 

 ing gradual changes of environment which react on the Odonate 

 fauna, as on other groups of aquatic life, resulting in time in the 

 disappearance of many of the original resident species and the in- 

 vasion of new forms better adapted to the altered conditions. 

 The drying up of water-courses, due to the clearing of the forests, 

 the pollution of streams and the filling of ponds and swamps are 

 also causing the disappearance of many species from the affected 

 localities, while other species previously unknown in the district 

 find suitable breeding-places in newly created bodies of water, 

 such as result from damming, streams, the construction of canals, 

 drainage ditches through swamps and along railways, gravel pits 

 and other excavations, etc. 



May, 1917 



