FAUNA OF THE CHESS AND GADE.- 



167 



usually found in clear water containing plenty of duckweed, and 

 this plant is very plentiful in both the pools mentioned, and 

 there is a large quantity in the moats. This explains, in no 

 small degree, the aforesaid agreement between the rofciferan 

 faunas. 



It is by no means easy, however, to explain the differences 

 in the rotiferan faunas, which differences can be seen best from 

 the following table : — 



Species. 



Langleybury 

 Pool. 



Parsonage 

 Farm Pool. 



Berkhamsted 

 Castle Moats. 



Colurus caudatus 



XXX X XX 



X 



X 

 X 

 X 



X 



x 



Diqlena biravhis 





Divlax triqona 





Eretmia cubeutes 





Flosctdaria campanulata 



x 



F. coronetta 



x 



Metopidia acuminata 





M. lepadella 



x 



M. oxy sternum 



x 



Noteus quadricomis 





Notommata lacinulata 





CEcistes styqis 





Philodina citrina 





Pterodina valvata 





Battulus rattus 





Botifer macrurus 





Stepha?iops lamellaris 



x 







Further collections might very well show that some of the 

 above species are common to two or all of the above-mentioned 

 waters. The table, however, represents the results obtained 

 from a large number of water samples collected at all seasons 

 of the year and during a period of nearly three years. It may 

 be, therefore, that the differences between the rotiferan faunas 

 of the pools of Langleybury and Parsonage Farm and the Castle 

 Moats are quite as great as the preceding table indicates. 



There are several differences between the pools mentioned 

 and the moats. In the first place, they are at different eleva- 

 tions, Parsonage Farm Pool being about 200 ft. higher than 

 Langleybury Pool and 100 ft. higher than the moats. Again, 



