﻿4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 59 



at Pacific Grove. Many of the maturer eggs hatched in the laboratory. 

 A number of female specimens collected on July n, 1906, at the same 

 place, carried eggs without eye spots. In a lot of eight females from 

 Little River near Trinidad, collected August 28, 191 1, seven carried 

 eggs, those from one specimen only showing the eye pigment. A 

 series of 35 females, from San Diego (date unknown), included 14 

 egg-bearing individuals, the smallest of which had a carapace length 

 of 11 mm.; four others were of practically the same dimensions. 

 This is apparently the limit of egg-bearing size. 



BURROWING 



While there are many burrowing species among the Crustacea, 

 Emerita and its allies show a degree of adaptation to this kind of life 

 far more complete than found elsewhere. To understand this we must 

 consider their peculiar habitat. Many burrowing forms live in mud 

 or sand in still water or at least in sheltered positions — Callianassa and 

 Upogebia — where a permanent hole is formed. Others, as the Can- 

 cridse, cover themselves in the loose sand or gravel in shallow water 

 or along sheltered shores. In Emerita, however, the method of food- 

 getting, to be described later, requires that they occupy exposed sandy 

 beaches exactly within the action of the waves. In this position they 

 maintain themselves near the surface. It is not easy to realize the 

 ceaseless activity necessary to keep this position. With every wave 

 the top layer of the sand is converted into a fluid which is swept by 

 the current with surprising rapidity. Any solid object in or on this 

 surface layer is at the same time undermined and shifted by the force 

 of the water. Every bather knows what insecure footing is furnished 

 by the sand in shallow water where the action of the waves is strong. 

 If the beach is carefully examined for several days in succession, it 

 will also be seen that the sand has been shifted, the movement often 

 affecting a layer several feet thick in a single day. As a result the 

 animal dislodged or uncovered by each wave must reestablish itself 

 to be in readiness for the receding wave from which its food is 

 obtained. 



As pointed out by Smith 7 their peculiar oval shape is well adapted 

 for burrowing in the sand. It is interesting to note that a shape super- 

 ficially very similar to that of the Hippidse appears in a very different 

 group, the Raninidae among the true crabs, which are also burrowing 

 forms. 



7 Trans. Conn. Acad., Vol. 3, p. 312. 1877. 



