1 82 BULLETIN OF THE BUREAU OF FISHERIES. 



mens. In a they are of about equal width, while in b the second area is much greater 

 than the first. The area between line c and the margin of the shell is in all three cases 

 very narrow, showing that, as the mussel approaches the adult size, further increase in 

 the shell must take place very slowly. The recovered specimen of Q. solida shows only 

 one broad area of growth, and a very narrow one around the margin. This mussel was 

 relatively much nearer adult size when put in the cage than the specimens of ventricosa. 

 Dr. Coker comes to the following conclusion with respect to the age of the specimens 

 of L. ventricosa: 



They are very significant, as they show clearly that grow'th is much more rapid than is generally 

 suspected. Considering what the gro^vth has been since the cages were put out, it is fair to assume that 

 the specimens had only one year's growth at that time. That is to say, they were glochidia in the spring 

 of igoy, and, since they must have been carried in the gills of the mother over the preceding winter, 

 their complete age at this time (Nov. 15, 1910) is a little over four years. 



Their age since the metamorphosis would therefore be about three years. Their 

 probable history, on the above assumption, is as follows: 



1. Eggs fertilized in August, 1906. 



2. Glochidia discharged in spring or early summer, 1907. 



3. Liberated from fish in summer, 1907. 



4. Collected at age (since metamorphosis) of about one year and placed in cages 

 June 29, 1908. 



5. Recovered and remeasured, November 15, 1910. 



The rate of growth of these individuals is probably typical of the genus Lampsilis, 

 and the experiment indicates at least that commercial mussels may reach a marketable 

 size in three years from the time they leave the fish. With the heavier shelled species 

 (those of Quadrula, for example) the rate of growth is probably slower and a longer 

 time must elapse before they are large enough for commercial use. 



These experiments, meager as they are, are quite significant and furnish the first 

 definite data, so far as we know, relating to the rate of growth of fresh-water mussels. 

 With the proper facilities and the opportunity of examining the mussels at closer in- 

 tervals, similar plantings could readily be made and exact information obtained on 

 the growth of all the important species. To prevent the cages from being buried in 

 the sand or mud would seem to be the chief precaution that should be taken in future 

 experiments of this kind. 



AN ARTIFICIALLY REARED MUSSEL. 



Another experiment, although it does not throw light upon the question of the rate 

 of growth in nature, might be mentioned in this connection on account of its significance 

 for the problem of artificial propagation. A lot of black bass which had been infected 

 with the glochidia of Lampsilis ligamentina, ventricosa, and recta at Manchester, Iowa, 

 on December 2, 1908, were brought to Columbia, Mo., and placed in a large tank con- 

 taining sand. The fish were left in the tank, where the young clams were allowed to 

 fall off in the hope that some would survive and be later recovered. The sand was 

 examined at intervals thereafter but never thoroughly, as the chance seemed very slight 

 that any of the young clams were still living. On December 26, 1910, however, a single 



