Handbook of Paleontology 127 



southern form {A. forbesii) occurs from low tide level 

 to a depth of 120 feet and may be distinguished from the 

 more northern form by the blunt-tipped arms and the 

 bright orange madreporic plate. A. vulgaris ranges from 

 low tide to a depth of 1200 feet. In color it may be beau- 

 tiful shades of pink or red, purple, yellow or brown. 

 Both species inhabit all kinds of bottoms. Other species 

 of this genus are common on the Pacific coast. 



Mollusks have several representatives that inhabit 

 tide pools. One of the very interesting forms found 

 is the Chiton or Armadillo Slug, with flat oval body 

 and back covered with eight shinglelike calcareous 

 plates. They cling with great tenacity to the surface 

 over which they are crawling, but roll up into a ball 

 when torn off. The common species of our coast 

 (Chaeto pleura (Trachydermon) apiculata) ranges from 

 Cape Cod to the Gulf of Mexico and is found not only 

 in rock pools left by the receding tide but on stones 

 and dead shells from below low tide mark. It is 

 abundant on dead oyster shells. The color is usually 

 dull brown or gray, but some specimens are white. 

 There are a number of very common' species along the 

 west coast, but comparatively few along the north and 

 along our coast they are small. In the Bahamas and 

 West Indies there is a large Chiton about three inches 

 long. The nudibranchs {Eolis, Doris) are likewise repre- 

 sented in the pools. 



Among the gastropods are the Rock Snails or Dog 

 Whelks {Purpura lapillus), the Periwinkles (Littorina 

 littorea and rudis) and the Limpets (Acmaea testudi- 

 nalis) found commonly along our shores. The Rock 

 Snail occurs in myriads on the rocks and in the tide 

 pools along the New England coast north of Cape 



