130 THE AMERICAN MIDLAND NATURALIST 
24%. While granting that the conditions of the experiment were 
somewhat unfavorable to growth, an impression gained by these inves- 
tigators was that thick shelled mussels, after they are half-grown, 
increased in size at the rate of Y4 in. a year or less. In summary, 
they state that the rate of increase in length of fresh water mussels 
varies from 1-2 inches in “paper shells,’ (Lampsilis laevissina), 
to 14, in. more or less in the “niggerhead,” (Q. ebenus), and related 
shells, while an intermediate rate of 34, in. or 1 in. per year charac- 
terizes the muckets and pocketbooks, (L. luteola and ventricosa), with 
a slightly more rapid rate for the yellow sand shell, (L. anodon- 
toides). 
Isely, (10), made a notable experimental study of the growth and 
migration of fresh water mussels. He collected some hundreds of 
mussels of various species, and after properly marking them and 
making necessary records as to their weight and dimensions, he 
returned them to their usual environment, reclaiming specimens at 
intervals for further observation, For 12 specimens of Q. lachry- 
mosa, undulata, pustulosa, rubiginosa, he finds an average per cent of 
aggregate gain of 13% in length, 1214% in height, 14% in breadth. 
Other data set forth by him will be referred to in discussion of the 
individual species dealt with in this paper. Howard, (9), attacks 
the problem of the growth of fresh water mussels from a_ broad 
biological standpoint. The length of juveniles of L. luteola growing 
in a floating crate at the end of the first growing season was ob- 
served to be 128 times that of the original juvenile at the beginning 
of free life. Depending most probably -upon the conditions of the 
season, by the end of\the second summer, these juveniles were found 
to have increased from 212-475% in length. As previous investi- 
gators had found, he observed that maximum growth was not attain- 
able under the best artificial conditions of culture. All these inves- 
tigators agree. that growth is most rapid in the juvenile period, 
decreases noticeably with age, in advanced years being almost imper- 
ceptible. 
It has probably become évident to the reader that the methods 
devised for the culture and propagation of mussels are so recent that 
at the present time and for some subsequent period, they will be 
unable to throw any light upon the rate of growth of these animals 
in their later years. For this reason, I believe that certain data of 
mine will upon analysis with fair qualifications add to our knowledge 
a 
