INVERTEBRATE BOTTOM FAUNA 



465 



sea-urchin {Echinus esaUentus), the hermit crab' {Pagiirus 

 bernkardiis), and a few other forms. Their occurrence is, 

 however, really due to their being surprised by the receding 

 of the tide, and they are not, strictly speaking, adapted to a 

 life in this area. 



There are some forms characteristic of the low-tide area 



Fig. 323. 



Metridiitm diaiifkus. VA\. (After Andres. ) '~ 



which cannot be regarded as belonging solely to any particular 

 facies. Perhaps the commonest are the sandhoppers (Gam- 

 marids), which have a wonderful knack of hiding themselves 

 quickly in holes and cracks, when the stone or other object, 

 under which hundreds may be sheltering, is removed. One 

 of the most abundant is Orckestia littorea, which, although a 

 true marine form, is able to exist for a long time out of the 

 water. I have found quantities of them during summer living 



2 H 



