Fresh-water Biology 



The General Plan of Part I 



The names of the genera that are included in the keys and illustrated in the plates are 

 set down in alphabetic order in small foot-tables facing the plates to which they corre- 

 spond. The Arabic numerals in the next column of the tables refer to corresponding figures 

 in the plate opposite: sub-numbers (as 12a) represent details, or variants within the genus. 

 Numerals within parentheses are used when no whole figure of the genus is given, and indi- 

 cate the whole figure of another genus that is similar in form. 



The length given in the next column is that of grown specimens, and is given in milli- 

 meters (one mm. equals 1/25 inch approximately). Maturity of nymphs of insects may be 

 judged by length of wing cases. The figures are for length of body without antennae and 

 tails. i 



The capital letters of the next column indicate continental distribution in a very general 

 way: N, E, S, and W; G, general; C, central. 



The last column gives habitat in terms of water movement: static (or lenitic) and lotic. 



In order to use the keys which 

 follow, choose between the alter- 

 natives offered and follow the nu- 

 merals in the margin on to the 

 name of the genus. Verify by ref- 

 erence to figures in the plate. 



If terms in keys are unfamil- 

 iar, use any good English diction- 

 ary. 



Recent studies have added 

 greatly to our knowledge of the 

 immature stages in the lower or- 

 ders of insects, and the keys in this 

 edition have been correspondingly 

 expanded. Too recent for incor- 

 poration here is the new and very 

 important work on aquatic dipter- 

 ous larvae by Dr. O. A. Johannsen 

 (Aquatic Diptera, in 5 Parts, 1934- 

 1938 in Memoirs of the Cornell Uni- 

 versity Experiment Station) com- 

 pleted as this left our hands for the 

 printer. 



For methods of caring for and 

 rearing aquatic animals consult 

 Culture Methods for Invertebrate 

 Animals, 590 pages, illustrated 

 (Comstock Pubhshing Co. Inc., 

 From Claassen , with alterations P rice $4. 00) . 



Antenna 



--Jlaxillary palpas 

 -- Labial palpus 



Labnim 



. _- Cl3T)eus 



.Ocellus 



- -.Compound eye 



— Occiput 

 .^.Pronotal disc 



--Marginal groove 



