FAUNA OF THE CHESS AND GADF. 421 



drying-up of the pools of course affects their faunas in a very 

 marked degree, and especially during the months referred to 

 above. It is evident that conclusions drawn from work done 

 during a series of a few years only may have to be modified in 

 the light of work done during another series of years. This 

 should be borne in mind when considering the following con- 

 clusions based on work done during the years 1912-1915. 



Ova-bearing females were particularly numerous in the 

 months of August, September, and October ; and although it is 

 not easy to decide which of these months gave the best results, 

 it seems that October yielded the greatest number. The pro- 

 portion of ova-bearing females as compared with all other adult 

 specimens of semdatus was, however, decidedly greater for 

 September than for either August or October. Some of the 

 pools furnished large numbers of ova-bearing females in June 

 and July, but on many occasions not one was taken during 

 these two months. 



• The . largest number for a single dredging and the largest 

 proportion of ova-bearing females was taken from Chipperfield 

 Common Pool on September 14th, 1912, when sixty-one ova- 

 bearing females and fifteen without ova were taken in one water 

 sample. From the same pool sixteen ova-bearing females and 

 fifteen without ova were taken on October 5th, 1912. Only a 

 small proportion of ova-bearing females was obtained from the 

 Pool on August 2nd, 1912, and August 8th, 1913, and on Sep- 

 tember 15th, 1913, Chipperfield Common Pool yielded no adult 

 specimens of C. semdatus ; on this last occasion the water was 

 low, brown, and turbid, and contained very few weeds. Very 

 many specimens were obtained from the pool, already referred 

 to, on Boxmoor Common on October 16th, 1912, and of these 

 ten carried ovisacs. From a pool near Shire Lane Farm, how- 

 ever, numerous specimens were obtained on October 15th, 1913, 

 and many of these had ova. Other collections which gave a 

 fairly large number of ova-bearing females, and deserve special 

 mention, were from the Gade, at Great Gaddesden, on June 3rd, 

 1913 ; Langleybury Pool, on June 18th, 1913 ; Chorley Wood 

 Common Pool, July 21st, 1913 ; Langleybury Pool, July 13th, 

 1915 ; and Parsonage Farm Pool, August 11th, 1912. Follow- 

 ing this last-named collection from Parsonage Farm Pool, 



