242 MR. E, 8. RUSSELL ON THE SHELL-GROWTH [ Mar. 2, 
5 mm., 41mm., and 2°5 mm. in length, but such small limpets are 
distinctly rare. They are of course extremely inconspicuous. In 
the autumn and during the winter limpets of about 10 mm. long 
gradually appear on the shore, settling down in greatest abun- 
dance in the months of January and February. There seems no 
reason to doubt that such limpets are only a few months old, and 
represent the first year-group. As the tables show they grow 
very rapidly (see Tables I. and V.) and can have taken only a few 
months to reach the length of 10 mm. It should be noticed that 
in very small limpets (2 
in proportion to the animal than in older limpets. If these 
limpets of about 10 mm. length represented not the first but the 
second year-group there ought to be found on the shore in spring 
and summer great numbers of shells from about 3 mm. to 7 mm. 
in length, and this is quite certainly not the case. Nor does it 
seem likely that the free-swimming larval life of the limpet is 
very long, or indeed longer than a week or two, for in the allied 
Acmea virginea the pelagic life is limited to a few days (Boutan). 
Acmea testudinalis, a much smaller shell than Patella vulgata, 
breeds from April to July and the season’s young are 4-5 mm. 
long in October (Willcox, 11). 
A random sample of 1003 limpets taken in July 1903 and 
1904 at Southend, Arran, show very clearly that this group of 
shells about 10 mm. long in January is really the first year-group. 
The sample was taken just at the very beginning of the breeding- 
season so that only a very few of the season’s young were 
included. 
Tasxe IT. 
Random Sample in month of July. 
Size in mm. No.. | Size in mm. No. 
| 3— 55... S| ESOS SiO met cee ao | 
6— 85... 9 | 39—41°5 50 
| 9—115 ... 26 | ADI sas spose 65 
VO VAS ii eeceedes 72 | 45—47°5 91 
| lit W/o 9 ae 102 | 48—50'd 83 
US =—PXORS caossecon ose 97 || ISS BPS) son ccsnscsns 77 
PPE TSY saanneeoeone 55 | 54—56'5 ......-..... 39 
DIM OIS scocaacstees eeu Whe “SISOB ssersccnan TD | 
[eye ee Gt ORE he se | 
[BOSS FS ccrssectache FAT Mas lh BSG an ta 1 
ly UBB ea SB io uc wile tsa! eumnCG = 6b; 5 seme nites amma 
The first year-group revealed by these figures has its mode 
clearly in the fifth class (15-17°5 mm.). Leaving out the first 
class (8-5°5 mm. shells), which represents probably the first of the 
season’s brood, and taking the next seven we find that tne mean 
value is 17°53 mm., indicating that limpets of the last season are 
