THE CRUSTACEA 119 



If kept submerged it will drown, and it may often be 

 noticed that at the time of very high spring tides the 

 sand-hoppers forsake their territory and swarm upon the 

 fields, rocks, roads, and even into the houses near the 

 shore. It seems to be a form which is, in the course of 

 generations, gradually forsaking the sea, to become a land- 

 dweller. 



At a somewhat lower level that is, where the tide covers 

 under stones, and under heaps of decaying sea-weed, may 

 always be seen in swarms the " Shore-hopper " (Oschestia 

 littorina). These two forms, Talitrus and Orohestia, are 

 classed as the Saltatoria (jumpers), all the other Amphi- 

 pods are swimmers (Natatoria). 



At the same zone as the last named, but also extending 

 to low-tide level, under stones and sea-weeds, in great 

 colonies, live the Grammarids. (The type of the Gammarids 

 is the common " fresh- water shrimp " of our brooks (Gam- 

 marus neglecta.) The common marine form is Gammarus 

 marinus. Its colour is olive-green, although individuals 

 that have lately changed their shell are pale brown. The 

 females are about twice the size of the males, as is the 

 case with all the Amphipoda, and a few of the Macrura. 



Under stones, lower down in the tide range, may be 

 seen the bright pink Mcera grossimana. 



Another one met with in the same places is Dexamine 

 spinosa. It has a strong, sharp, projecting point on the 

 edge of each of its segments, so that when it rolls up, as 

 it always does when at rest, it has the appearance of a 

 little circular saw. Its colour is white, delicately spotted 

 with pink. 



In cracks of rocks in dry situations, where sand has 

 filtered in between, is a curious form, in which the antennae 

 are modified into grasping organs an unusual modifica- 

 tion. This is Corophium longicorne. Its colour is porcelain- 

 white. 



