rJo'J MR. C. S. ELTON ON THE 



2. I'liE Mixes of Railway Ditch, Oxfoko. 



If tliere are no particular Liws governing the occurrence of 

 colours in uiites we should expect to lind chance mixtures of 

 colours among the species of any one habitat. In the following 

 example such was clearly not the case. During May 1921 the 

 fauna, cf a, small ditch near Oxford (here referred to as " Railway 

 Ditch "') was examined by me. This ditch is connected by 

 several channels with the Tiiames, but is usually almost stagnant. 

 Only one part of it was studied, an area about 30 yards long and 

 4 feet wide Since it is important to know Avhat animals and 

 plants are associated with the mites, a list of the species observed 

 during the course of the work is given below. This list is not 

 by .any means exhaustive, but gives some idea of the type of 

 habita,t in which the mites were living. 



Plants : Banunculus aQitatiUs Agg., Hottoula palustris L., Calli- 

 triche aqnatica Sm., Potamogeton natans L., P. perfoliatus L,, 

 P. densiis L. [Lemiia minor L., L. trisulca L.). 

 HiRUBiNEA : Two large species. 



MoLLUSCA : Limncea stagnalis L., L. peregra JMiill., Planorhis 

 corueus L., P. complanatus L., P. spirorbis MiilL, Ancylus 

 laoicstris L., Bithynia tentaculata L., Paladina vivipara L. 

 Insecta : 



Coleoptera: Di/tiscu.s marginaUs L., Hi/phrydus ovatus L., 

 Hydroporus palustris L., Agalnts hipustulatus L., Haliphis 

 sp. 

 Hemiptera: Xepa ciuerea L., Hydrometra stagnorum L., 



Notonecta glauca L., Corixa sp., Velia sp., Gerris sp. 

 N 6 u r o p t e r a : Various larv:^. 

 Crustacea : Cyclops serraiidus Fischer, C. prasinas F. 

 Chydorus sp. 

 Aselliis aquaticus L. 

 Fish : Gasterosteus acaleatus L. 

 Amphibia : Frog tadpoles. 



The mites and their colours are shown in Table I. 



Table I.— The Mites of Railway Ditch, lilay 1921. 



Species. 



CoLori?. 



Sj/drarachna (jlohosa De Goer. 



Scarlet. 



JBT. schneideri Koeu. 



Scarlet. 



S'. distlncta Koeu. 



Scarlet. 



S.fuscata Soai-. 



Dark purple with reddish spot on back. 



Sylais Itamata Koen. 



Scarlet. 



Diplodontus despiciens Miill. 



Scarlet. 



Hi/dri/pJianfes rxher De Geev. 



Scarlet. 



JPioua loiiffip>alpis Kreiid. 



Scarlet with black spots on back. 



Limnesia fidgida Kocli. 



Scarlet with blact marks ou back. 



