The ierican Midland Naturalist 
PUBLISHED BI-MONTHLY BY THE UNIVERSITY 
OF NOTRE DAME, NOTRE DAME, INDIANA 
VOL. VIII. NOVEMBER, 1922. NO. 6 
Observation on the Rate of Growth of the Shell of Lake Dwelling 
Fresh Water Mussels. 
N. M. Grier, PH. D. 
Washington and Jefferson College, Washington, Pennsylvania. 
I. —INtTrRopUCTION AND STATEMENT oF PROBLEM. 
Nearly all our present knowledge of the rate of growth of fresh 
water mussels is confined to studies of the development of juvenile 
mussels through the period of infection by the glochidia upon the 
host fish to a time not exceeding six years thereafter, the rate of 
growth of the animal being most conveniently determined by the rate 
of growth in length of its shell. Portions of these studies having a 
direct bearing upon the subject of this paper are now cited. 
Curtis and Le fevre, (14), indicate that juveniles of Lampsilis 
ventricosa first observed in the second year of free life, may nearly 
double in size by the close of the fourth year of growth. Coker, 
Shira, Clark and Howard, (2), reporting upon pond raised specimens 
of Lampsilis luteola remark that four additional growing seasons are 
required for such shells to double in length after the second growing 
season. Lampsilis gracilis, a thin shelled species, was found to 
increase in length at the rate of about 190% a year. They add 
that since these species are all mussels of river habitat, it can not be 
assumed that growth in ponds is representative of the rate of growth 
in a natural environment. They then record an experiment with 
principally thick shelléd, (Quadrula), mussels, which were placed 
in a crate in the Msisissippi river for nearly one year. None of 
these mussels were over three inches in length, and after 10 months 
and 12-days had increased in length as follows: Q. ‘ebenus, 3%; 
Q. pustulosa, 5%; Q. metanevra, 9% ;.Q. plicata, 8%; Q. undata, 
