MARINE BIOLOGICAL STATION ON PUFFIN ISLAND. 29 



additions to the list of species. Those collected during 

 the " Hysena" expedition will be referred to further on. 



Protective Colouring. 



The important and now popular subject of the relations 

 existing between the forms and colours of animals and 

 their environment has received a good deal of attention 

 at Puffin Island, and various instances of protective and 

 warning colours have been noted in the reports. There 

 are two additional cases of ' 'procryptic" colouring (according 

 to Poulton's excellent system of nomenclature) which 

 seem worthy of record, viz., the small flat-clawed crab 

 Porcellana platycheles and the Annelid Eulalia viridis. 



P. platycheles is very common on the shores of Puffin 

 Island and is generally found on the under surfaces of 

 irregular fragments of carboniferous limestone. A dozen 

 or more specimens may be exposed on turning over a large 

 stone, but until one is aware of the concealment, the crabs 

 are so inconspicuous that they usually escape notice. They 

 place their flat bodies in slight depressions on the stone, 

 and the dirty greyish-brown colour of the carapace cor- 

 responds exactly with the muddy surface of the decay- 

 ing limestone, while to still further aid this protective 

 resemblance, the strong hairs with which the limbs are 

 fringed entangle mud particles and other foreign bodies 

 and so help in grading off the body of the crab into the 

 surrounding stone. And then the habits of the animal 

 come in : P. platycheles is a peculiarly sluggish crab, and 

 certainly in many cases its salvation must depend upon 

 lying quiet. When the stone is turned over the crabs 

 usually "sham dead " or rather, in this case, " sham rock," 

 and so long- as they remain motionless are very incon- 

 spicuous indeed. It is obvious that in such a case the 

 more sluggish the animai is in time of danger the greater 



