C. B. Davenport 



15 



at places where it is submerged for only a short time at high tide and then under 

 water that is nearly fresh. Littorina rudis behaves similarly in other parts of the 

 world. Thus Fischer (1887, p. 182) states that at Trouville (Calvados) on the English 

 Channel he has found L. rudis on rocks two meters above the other marine animals 

 and moistened only by the highest tides. In fact, according to Simroth (1891, p. 84), 



Fig. 7.— Photograph taken at half tide from the base of the sand spit, looking east, showing inner harbor, 

 the hook of the spit, and the gut beyond. 



species of Littorina pass the winter out of water with their gill chambers full of air. 

 Littorina rudis, then, has evidently progressed far on the road toward adaptation to a 

 terrestrial life — a road that the Pulmonata must have traveled long ago. 



C. THE INNER EDGE OF THE SAND SPIT 



Along the whole length of the inner beach, not far from the high-tide line, occur 

 the holes of the fiddler crabs. These crabs belong to two species, namely, Gelasimus 

 pugnax and Gelasimus pugilator. A remarkable thing in the distribution of these 

 species is the fact that although their habitats are not markedly different their areas of 

 distribution are so well defined that they hardly overlap. Both species occur at the edge 

 of the Spartina. The pugnax is found all the way from the western, proximal end of 



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