1913] 
Pearse: Fauna of the Rock Beaches 
33 
Cancer irroratus were also common. Mytilus formed large beds. 
Many drilled shells were strewn about; Polineces heros was repre- 
sented among these, though none of this species was seen alive. 
The surface of the mud flats became very hot when the sun 
beat down upon it at low tide. Many animals crawled under 
the eel-grass for shelter or burrowed in the sand ( Nassa ). Car - 
cinides often burrowed and emerged again with a little disc of 
moist sand on its back thus securing protection from the direct 
rays of the sun. 
Except for certain worms, Mya , and Limuius, no species is 
found on the mud flats that does not appear on other beaches. 
The dominant animals are Carcinides, Littorina litorea, Mytilus , 
Crago, and Lumbriconereis (?). All but the last two are numerous 
on the rock beaches. The only abundant organisms that do not 
Fig. 30. Part of a Dead Lobster Covered with Littorina litorea ; on 
the Mud Flat. 
Fig. 31. Limuius polyphemus. 
The female has excavated a hole and the male waits above her to ferti- 
lize the eggs she will lay. 
occur on both the rock and mud are the large littoral algae, sponges, 
hydroids, and Bryozoa, which are absent from the latter. The 
dropping out of certain animals on mud flats is doubtless due to 
the lack of suitable objects for attachment and the comparative 
impurity of the water. The animals that are unable to live above 
the mud, like crabs and Littorina, have special arrangements for 
respiration {Mya, Nassa), except the worms whose soft bodies 
makes aeration of the internal fluids easy. 
