REPORT OF COMMISSIONERS OF INLAND FISHERIES. 55 



of growth, usually present on the shell, are not by any means a "re- 

 liable way of determining the age of the specimen. These rings are 

 due to the rubbing and breaking of the fine edge of the shell from 

 any cause whatever; they are liable to be repeated at any time 

 within a few months, and, on the other hand, they may not appear 

 at all, even in clams which are much more than a year old.* 



Distinct rings are always produced when a clam is taken and al- 

 lowed to burrow again in coarse sand or gravel. We have often pro- 

 duced the ring in this way and also by wearing off the edge of the 

 shell by running a file over it. It was this observation, indeed, 

 which suggested the following simple method of indelibly marking 

 the clams. A small notch is filed into the edge of the shell and the 

 clam returned to the soil. As it grows the notch remains perfectly- 

 distinct and always at the original distance from the hinge. When 

 the clam is again examined the notch identifies it as the one which 

 was planted, and furthermore indicates the amount of growth. A 

 growth ring usually accompanies the notch, and so, after a month, or 

 even years, the complete outline of the clam at the time of notching 

 can be readil}'^ identified and traced upon the shell of larger growth. 

 The device allows greater freedom in distributing experimental seed 

 clams, and provides, at the same time, perfect accuracy in the re- 

 sults. Figs. 8, 9, 10, and 11. 



Experiment Upon Rate of Growth. — The following brief account of 

 some experiments and observations, made during the past few years, 

 gives numerous examples of the sizes of clams at different ages, and 

 illustrates also'the variability in the rate of growth. As far as possible 

 the general statements and the statistical tables will be given sepa- 

 rately . 



Experiment No. 1. An exceedingly thick set of clams, discov- 

 ered in July, 1899, on the southernmost point of Cornelius Island, 



* Fig. 12 illustrates this point. It is from a life-size pliotograph of a clam one year and 

 three months old, three inches in length, which, from July 18, 1901, to September 10 of the 

 following year, lay buried in a land tile which was set perpendicularly in the ground. This 

 specimen was not disturbed during this time, and no growth rings are visible on the shell. 



