172 



NATURAL HISTORY OF OUR SHORES 



but all the other limbs are short. Its colour is olive- 

 brown. It is found under stones in rocky places. The 

 surface of the shell is scantily furnished with hooked 

 bristles, but its surface is of such texture, like terra-cotta, 

 as to afford the correct conditions for spores of weeds to 

 adhere and develop. (I have not known this observed, 



Fig. 78. Pisa Gibbsii. Male and Female. The latter is decorated with branches 

 of Polyzoa. Natural size 



but the same thing obtains in another genus (Inachus), 

 which does not decorate itself, but upon which sponges, 

 ascidians, etc., are always found growing.) 



Pisa Gibbsii (Fig. 78) is a species that is often found in 

 the littoral, in the same situations as the last viz. under 

 stones in rocky districts although it pertains to deeper 

 water. It has a general resemblance to the last, but is 

 more angular, and the back is covered with a fine coating 



