C. B. Davenport 



between average tides. On the inside of the spit, on the other hand, the marsh grass, 

 Spartina, finds abundant foothold. All these facts have an important influence on 

 the distribution of the animals of the sand spit. Indeed, for the purposes of this 

 account of the fauna of the spit it will be necessary to treat separately its outer and 

 inner margins and its tip, just because the conditions are so different in the three 

 situations. 



r**fT3 



mm 



Fig. 3. — View of sand spit taken near western end looking east. Terrestrial border zone with Ammophyla in the 

 foreground. The outer beach with the storm bluff, wreckage-strewn upper beach, and lower beach. At the right the 

 inner beach, passing into mud flats at the edge of which Spartina polystachya is growing. 



A. ANIMALS OF THE OUTER BEACH 



The outer beach may, for our purposes, be divided into three zones which we 

 may herein designate as : (1) the submerged zone ; (2) the lower beach ; and (3) the 

 upper beach. The submerged zone includes all that portion of the beach that lies 

 below mean low tide, but which may be exposed by the lowest spring tides combined 

 with southerly winds (Fig. 4). It is a region that is normally covered with water ; it is 

 the very margin of the shallow sea. The lower beach is that zone which lies between 

 mean low tide and mean high tide. It is the zone that is twice each day exposed to 

 the air and submerged. It passes without any sharp break into the submerged zone 

 (Figs. 4 and 5).- The upper beach is limited on the one hand by the line of debris that 

 marks the average high tide, and on the other by a bluff, half a meter high, that has 

 been cut by storms (Fig. 5). 



159 



