138 THE AMERICAN MIDLAND NATURALIST 
LASMIGONA COSTATA ERIGANENSIS. 
5. 
No. ; 
Spec. Age 1 DVD DSD PD AD Shi NSIC, IMSL 
7 6 7.41cem. 4.05cm. 2.59cem. 5.50cm. 1. 9cm. 3.62cm. 1. 7cm. .21cm. 
2 7 101% 105% 106% 105% 90% 109% 94% 124% 
2 8 113% 118% 113% 114% 116% 85% 205% 109% 
2 e224 lS ae SoZ MOS 95% 122% 103% ~124% 
2 TO; WAG NIA F069 NZ 96 NG ee 2475 91% 100% 
Average growth per year in each dimension for 10 years, (oldest shell), 
4% 5% 4%: 44% - 1.6% 4% 9.2% 716% 
Average growth per year in each dimension for 5 years, (6-10 yrs. inclus.) 
10% 124% 94% 11% 4% 10% 23% 19% 
DepucTIONs FROM TABLE OF PERCENTAGES. 
As the few shells of the series obtainable are somewhat advanced, 
it is not easy to draw satisfactory conclusions concerning their rate 
of growth. However, DVD, PHL and TH increase most rapidly, 
the large increase in AHL is probably accidental. Increase in thick- 
ness is not so well marked. 
Fr 6. ANODONTA GRANDIS FOOTIANA 
oO. 
Spec. Age L DVDr SD |PAD) AD> IPH ALES hii 
5.27cm. 3.27cm. 2.24cm. 3. 6cm. 1.65cm. 2. 3cm. 1. 3cm. 1.4cm. 
142% 127% 143% 144% 140% 130% 138% 107% 
175% 165% 174% 169% 138% 184% 169% 157% 
166% 151% 156% 175% 145% 170% 147% 121% 
160% 150% 133% 166% 148% 112% 137% 128% 
163% 170% 180% 196% 168% 184% 160% 128% 
Average growth per year in each dimension for 9 years, (oldest shell), 
34% 29% 32% 39% 27% 31% 28% 16% 
Average growth per year in each dimension for 5 years, (5-9 inclus.) 
1% 53% 57% 70% 48% 56% 50% 28% 
WB Qo = — 
OmBNAWND 
DepucTIONsS FROM TABLE OF PERCENTAGES AND REMARKS. 
The greatest increase in the years represented is in the dimensions 
of PD, DSD, PHL. The latter appears to enlarge uniformly. It 
is noted that shells may be as large at 6 years as at 9; the relative 
increase in thickness is apparently small. Isely, (10, p. 15), made 
studies of the parent species A. grandis. The nearest specimen to his 
I studied and no larger one, was aged 9 years. It showed an increase 
of 3% in length, 20% in height, and 47% in breadth over the 
average for 8 year specimens, against 4%, 3.2% and 6.7% in Isely’s 
specimens. The tremendous increase in inflation is undoubtedly due 
to the lake environment, the greater height of my specimen seems 
to be that of an unusual variant, since the height Isely gives may be 
obtained in my material by selection of the variants. 
