432 University of California Puhlications in Zoology [Vol. 16 



normal animals, but in attempting to burrow could succeed in only 

 partiall}' covering their bodies. 



By dropping small quantities of ink into the water I found the 

 current through the gill chamber always passing from the posterior 

 to the anterior end as a finely rhythmical flow, nor was I able at any 

 time to discover a change from this habit, though Wej-mouth and 

 Richardson say that the direction of the current regularly reverses. 

 When at rest the position of the animals in the sand is alwaj'S with 

 the posterior end downward. Their presence is revealed only by V- 

 shaped ripple marks made by the spreading antennae in the thin film 

 of water that runs down the sand following the dash of each wave. 

 Seldom do the animals betray their presence in any other manner. 

 If a person approaches a bed of sand-crabs the antennae are all with- 

 drawn so that concealment is most complete. Stamping had the effect 

 of producing slight disturbances in the crab beds. These disturbances 

 were probably due to the crawling of the animals deeper into the 

 sand. If one stands for some time in the midst of a bed of sand-crabs, 

 the creatures remain concealed in the sand for an indefinite time. 

 After one withdraws from the vicinity of the bed, apparently the 

 original number reappears. Tossing a spade into a bed of crabs had 

 practically the same effect, excepting that they reappeared sooner 

 than when one stood in their midst. 



This concealing action strongly suggested that the animals are 

 frequently the prey of certain beach birds. I suspected the herring 

 gulls, but at no time saw the gulls feeding upon them, nor could I 

 learn from fishermen that such was ever the case. Soon after, how- 

 ever, I noticed flocks of sandpipers and long-billed curlews feeding 

 ravenousl.y upon the crabs and concluded that the concealing reaction 

 is due to the feeding of these birds. 



Emeritae are usually found in the zone of the beach washed inter- 

 mittently by the waves. I could see no evidence of their presence in 

 the sand above this zone, although I examined the region carefully. 

 According to Barnhart, they occur in the sand well out beyond the 

 line where the waves strike the beach. Inasmuch as the food of the 

 animals consists of organisms which they entrap with their feathered 

 antennae from the water as it moves to and fro (Wejonouth and Rich- 

 ardson), it seems that for this reason they seek those regions where 

 the waves cause a to-and-fro movement of the water. 



Here, then, was a complex reaction based upon (1) a to-and-fro 

 movement of the water combined with (2) the burrowing habit. In 



