328 THE AMERICAN NATURALIST. (VoL. XXXIX. 
twenty years before on the northern shore of the Isle of Man, 
where it is still to be found. In view of these facts it would be 
very interesting to learn whether it is moving southward on our 
own coast. 
Distribution of the adult animal is probably effected not only 
through its own locomotion but also by the aid of tides and cur- 
rents. On one occasion, though only on one, I found a limpet 
crawling back downward on the surface film like a fresh-water 
snail but I have not very infrequently found them clinging to 
floating pieces of the larger Floridie, upon which they feed. It 
will be remembered that Nacella and Helcioniscus live habitu- 
ally upon the large fronds of Macrocystis. © Occasional trans- 
portation of the adult by such means may not impossibly be a 
more effective factor in its distribution than the brief pelagic life 
of the young, which Boutan found in the case of A. virginia to 
be limited, at least in the waters of Roscoff, to a few days' dura- 
tion. 
Locomotion is almost exclusively effected by crawling over 
the substratum. Progress is exceedingly slow ; the fastest crawl- 
ing of which I have record was at the rate of about three inches 
per minute. This was in a tide pool where the animal was un- 
disturbed and in natural conditions. Under such circumstances 
it often remains motionless for hours. In captivity it is not 
unusual to find one limpet crawling over another or adhering 
to its shell, although in such circumstances I have never 
observed either individual showing any recognition of the pres- 
ence of another of its own kind. 
In view of the well known homing habits of Patella and of 
the fact that I have found the same power possessed at least in 
a limited degree by animals so widely separated as Fissurella 
barbadensis Gmelin and Siphonaria alternata Say, I have made 
repeated attempts to satisfy myself of its existence in Acmza. 
These attempts have, however, been unsuccessful. The diffi- 
culty lies in the character of the rocks of the New England 
coast, which are unsuited either to the formation of a sunken 
" scar" like that which indicates the home of Patella or of a dis- 
colored spot like that produced by Siphonaria. It is therefore 
impossible to locate with certainty the * home" of a limpet, which 
