1922] Setchell,——Cape Cod and the Marine Flora 9 
(exposed to the full outer temperature through the inward cold 
currents of *'The Race") are, and ought to be expected to be provided 
with waters of a temperature of 20? C. orless. Even if these portions 
of the coast are somewhat affected by the warmer waters from within, 
the deeper waters are colder and, consequently, we find that the 
northern species are frequently found in water of one to thirteen or 
more fathoms in these areas, whereas north of the cape the same species 
may occur in the litoral, or at least in the uppermost sublitoral belt. 
It seems that there is a scanty northern flora in the deeper waters even 
of the interior of Long Island Sound itself. 
I have prepared a map showing the probable details of the deflection 
of the 20? C. isothere inwards and its enclosure of the inland waters 
eastward from its approach to land from the outer waters. It passes 
along the coasts of eastern Connecticut outer coasts of Rhode Island, 
and southern and southeastern coasts of Massachusetts, and its posi- 
tion illustrates the general relation, at least, of Cape Cod to this 20* C. 
line of mean maximum temperature. This map and its temperature 
lines show that the district between Chatham, Massachusetts on the 
east and New London and Montauk Point on the west, belongs to the 
North Subtropical Zone so far as the inland or sheltered waters are con- 
cerned and more or less normally to the North Temperature Zone, so 
far as the outer points and even whole ranges of the shores exposed to 
outer waters are concerned. The outer waters seem to be somewhat 
affected by the inland warmer waters in their immediate vicinity, 
however, because the northern species occurring in them either tend 
to grow in deeper water than they do north of the cape, or are often 
reduced, or even depauperate. It seems best, therefore, to regard the 
latitude of Provincetown, as Collins has done, to be the dividing line 
between the North Temperate and the North Subtropical Zones on 
the Atlantic coast of North America. The shores to the south, then, 
even including the deeper waters of Long Island Sound, show a very 
considerable admixture of northern species flourishing even during 
the season of normal maximum temperature. In this connection, 
attention may be called to the fact that the whole coast of New Eng- 
land lies between the mean maxima, or winter, temperatures of from 
0? C. to 5? C. and is therefore subject to seasonal invasion, or, in the 
case of hardy perennial species, of winter or spring fruiting, of species 
normal to the Upper and Lower Boreal Zones. A discussion of these 
species would be of great interest, but is only of importance in a 
