INLAND FISHERIES. 87 



surface agaiu, as if dissatisfied with the suiTcjiinding's, and, after 

 wandering about for a short distance, once more g"o down. This 

 process I have known to be repeated, in an individual 6 milH- 

 meters in length, half a dozen times in the course of three days. 

 They seem to wander short distances — one or two inches only — 

 between the periods of descent, Ijut I have noticed it in few cases, 

 and perhaps the wanderings on the surface of the bottom may at 

 times be more extensive. How large the clam is before it finally 

 digs into the bottom to remain permanently, I am not able to say. 



1 have frequently found lying on the surface empty shells at least 



2 centimeters long which had been perforated by the oyster drill 

 ( Urosalphix), which could only have made its attack when the 

 living clam was out of its burrow. Clams of this length, then, 

 apparently have periods of wandering, and it would be interesting 

 to determine, if it were possible, whether or not they would be able 

 to move up between the tide marks from some position below low 

 tide. When dug out of the bed, clams measuring 2 or 3 centimeters 

 in length are generally found to have gone down 12 or 15 centi- 

 meters (5 or G inches) from the surface, the extremely delicate and 

 filmy siphons of the small individual becoming relatively larger 

 and more muscular. There undoubtedly comes a period — probably 

 not far from this time — when the clam ceases to come to the sur- 

 face, and, except for some accident, remains forever buried, reach- 

 ing up to the water only by means of the siphon tubes. Evi- 

 dence of this we have in the fact that clams are frequently to be 

 found between rocks in such a position that it would be impossible 

 for them to move, having reached such a location when smaller. 

 Then, too, shells, especially the larger ones, are frequently dis- 

 torted and rendered asymmetrical by coming in contact, in growth, 

 with an unyielding object, such as a stone. The shape in such 

 cases conforms to the space in which movement is possible. This 

 same distortion of the shell may be noticed in other burrowing 

 lamellibranchs, like Petricola pholadiformis. In the case of this 

 latter form, and also in Pkolas trimcata, which are to be found 

 buried along the edges of salt marshes, the burrow is seen to be 



