— 21 — 



shell may be broken or partially pulled off before the foot is torn out 

 of the sand. Small specimens dug out at Oeeano buried themselves 

 with eight or ten thrusts of the foot, a process taking in one case seven 

 seconds from the time the clam, lying on the surface, first thrust out 

 its foot until it disappeared. In fact the burrowing reaction is so 

 deep-seated that when a small clam is cut in two by the shovel, the 

 foot-bearing half will still rapidly bur_v itself. These details of its 

 habits are given to show how a fragile-shelled clam may maintain 

 itself, escaping, by its rapid and deej) l>urrowing, the surf and the 

 scouring of the waves. 



Neither of these forms is found in the lagoon ; even if transplanted, 

 the Pismo clam will not live long in the quiet waters of a bay. The 

 reason for this, our ignorance of its habits and needs does not permit 

 us to answer, but the fact is well established by the experience of the 

 clam diggers. These two species are the best examples found in 

 California of the group of active burrowers previously mentioned. 



Along the spit, particularly at the tip, in the shelter of the bar are 

 found large numbers of a small clam, the wedge shell {Donax 

 hici'igata) very much in superficial appearance like a miniature edition 

 of the Pismo. It lias a firm stout shell and short siphons and, when 

 feeding, is not buried l)ey()nd its own depth; since it seldom equals an 

 inch in lengtli, this leaves it at the surface. Its burrowing powers must 

 l)e correspondingly great but it will be noticed that it is more abundant 

 in slightly slieltered locations and often it is washed out and piled 

 in \vindrows l)y the storais. 



A diligent search shows no other forms alcove the low tide level on 

 tlie outside. Within the lagoon the bottom is varied, as may be seen 

 from the map. On the north side of the entrance and in the bight 

 on the north in front of the summer cottages of Anaheim Landing, the 

 sand is underlaid at varying depths by hard clay and farther along 

 by a stiff blue mud. 



This bottom, which can not readily be washed out or shifted, shelters 

 a number of boring forms which offer good examples of bivalves found 

 in permanent burrows. In the hard clay is found tlie piddock 

 (Z'irfaca), while fartlier along where the clay passes into mud are 

 found many of a less truly boring form, riatijodon. All of these 

 agree in occupying holes from which they never voluntary move and 

 indeed could not move, as the hole in the clay is only large enough 

 for tlie siphons, and far too small for the shell. Their only movement 

 is the slow grinding apparently brought about l^y twisting the rough 

 shell in its liole, which serves to enlarge the burrow toi the extent 

 required by the growth of the clam. From these safe shelters, in 

 which tlieir relatively thin and fragile shells are well protected, they 

 thrust out siphons of a surprising length from the clay hole through 

 the overlying sand. Wlien one has dug through two or three feet 

 of water-saturated and flowing sand, following the slender retreating 

 siphons, Tie is willing to believe what is obviously impossible, that the 

 clam is digging away, and he is thoroughly convinced that the clams 

 are safe from all harm except the possible biting off of the siphon 

 tips. The creek does not offer this kind of iKjttom at any other place 

 and at no other place are the borers found, being quite incapable, 



