92 



THE SCOTTISH NATURALIST 



The Water-Beetles of the Ballast-holes — continued. 



Anacana globulus . 

 Hydroporus hicogmtus 

 Colymbetes fusciis . 

 Haliplus ruficollis . 

 Hydroporus palusiris 

 Hydroporus erythrocephalus 

 Gyrinus nataior 

 Helophorus brevipalpis 

 Haliplus wehnckei . 

 Hydroporus palustris 

 Agabus arcticus 

 Ilybiiis fuliginosiis . 

 Ilybius cenescens 

 Dytiscus punctulatus 

 Hydroporus lituraius 

 Agabus nehulosus . 

 Dytiscus marginalis 

 Acilius sulcatus 

 Laccobius minutus . 



'- 2 



The number of occurrences of each 

 species in the twenty-three ballast-holes 

 examined. 



Agabus clialconotus 

 Haliplus linealocollis . 

 Agabus nebulosus 

 Helophorus agualicus . 

 Hydroporus nigrita 

 Philhydrus fuscipennis 

 Agabus bipustulatus 

 Hydroporus gyllenhalii 

 Dytiscus fuarginalis . 

 Hydroporus pubescens . 

 Hydroporus lituraius . 

 Ilybius fuliguiosus 

 Rhantus bistriatus 

 Hydroporus obscurus . 

 A nacana globulus 

 Hydroporus erythrocephalus 

 Hydroporus palustris . 

 Agabus arcticus . 

 Gyrinus natator . 



% 

 35 



33 

 32 



29 

 26 



25 

 21 

 20 



i8 

 17 

 15 

 14 

 13 



lO 



The number of occurrences of each 

 species as a percentage of the total 

 number of occurrences of the species in 

 the island. 



Now these pits in the clay at first form an ordinary fresh- 

 water pond type of habitat, since they are filled with rain- 

 water, and there is a complete absence of acidity. Some of 

 them appear to pass very rapidly to the acid-water type, 

 small patches of Sphagnum developing at their edges, and 

 gradually spreading over them, while others first become 

 overgrown with glyceria, and pass more slowly over to the 

 Sphagnum pool ; but even in ponds thick with glyceria the 

 water, after a time, becomes deep brown in colour, suggestive 

 of peatiness. 



{To be continued.) 



