22 



Nils Rosén 



{N. tesselata) with the characteristic blood red blotch inside the aperture, and another 

 form with a black opercle. These two last-named forms of Nerita occur throughout 

 the range of these ragged rocks, even on the outside, where the breaking of the 

 waves are very heavy. The Neri tas are always attached with the foot, not by 

 means of any secretion, which would not do in the strong currents caused by the 

 flowing tide. They are much more dependent on the water than Tectnrius, and 

 cannot live for any considerable time out of water as these do. Several specimens 

 were brought to the place where the specimens of Tectarius live, but they all died 

 rather quickly. Tectariits on the other hand is not able to stand the heavy rolling 

 of the sea to which all animals in the region c are exposed. An experiment showed 

 that they were washed away, if they had not already crept up to the more quiet 

 region. On the outside of this region large Chitons and barnacles are also found. 



A quite sterile region (d) follows tlie preceding. The ground is flat, consisting 

 of coral sand, very tightly packed, but not cemented to limestone. No algtc are 

 found here and animal beings are also wanting, except some shells accidentally 



Fig. N. Section through a rocky shore, showing the regions of the Fauna. (See text.) 



occurring. This is the region where the force of the waves, when the tide flows 

 seems to be strongest. I think that the absence of Neritas and Chitons here is 

 due rather to the lack of sea weed and other organisms on which they feed, than 

 to defective power of standing the waves. 



A varying animal life characterizes the broad area which is the last region 

 that is influenced by the tide (e). Coral sand, hardened almost to rock, covered 

 with low algfe forms the ground. Holes in the ground are numerous as well as 

 loose rather large pieces, due to an undermining of the hard sandy rocks, 

 or pieces of corals, thrown up by the waves. At high tide this area is entirely 

 below water, but at low tide the upper surface is laid dry, the water however 

 remaining in the holes and under the stones. In tlie rocks several polychœts. 

 (Sal)ellids and others) and Gephyreans burrow. Sea-urchins excavate the rocks, 

 Holothurians, both small and of a medium size, ophiurians and a great number of 

 shells, as Purpura, Conns, are found under the rocks. Several forms of crabs occurt 

 the large blue crab (Calinedes), rock crabs (Pilumnus), spider crabs and a grea. 



