DISTRIBUTION OF THE SHELLS OF FLORIDA. 581 
standing the comparatively recent origin of the peninsula 
which separates them. 
Of the recent origin of the Floridan peninsula (or at least 
of the northern part which makes the separation between the 
great Carolinian Bay and the Gulf of Mexico), we have not 
only geological but zoólogical evidence. Although, as shown 
above, the littoral fauna * of that part of the gulf which 
bathes the west coast of Florida is of a character far more 
tropical than that of the east coast, the fauna of the latter 
is reproduced in the northwestern part of the gulf. The 
correspondence between the shells of Galveston and those 
of South Carolina was noticed by Roemer many years ago, 
and the fact is now confirmed by an examination of the 
shells brought by Dr. Durham from several points on the 
coast between Point Isabel and Pensacola. The peninsula 
and warm waters of the southern cape of Florida now form 
an impassable barrier to the western migration of species of 
the temperate fauna into the colder parts of the gulf, but of 
their connection within a comparatively recent geological 
period there can be no doubt. The connection was probably 
through sandy straits and lagoons, too shallow to allow of 
the passage of the gulf-stream, but perhaps permitting the 
westward flow of the cold waters of the Carolinian Bay. 
The present tropical character of the shells of the west 
coast of Florida is plainly due to the influence of the gulf- 
stream, which is not here, as in the northwestern part of 
the gulf, crowded off the shores by the waters of a great 
river, or by cold northwest winds. On the other hand the 
east coast, as far south as Cape Canaveral, forms a part of 
the shore of the Curolinian Bay, along which, inside of the 
guif-stream, a cold current runs, giving to this part of Flor- 
ida a coast fauna similar to that of South Carolina. 
* By the littoral fauna, that of the true ocean shores is here meant. The waters of 
the shallow inlets "rer estuaries of the west coast are subject to great changes of tem- 
perature, which, dar ing the w inter *morthers," may fall to the freezing point, at 
Which times fish ca s > i t numbers i expected, 
; mig 
the fauna of these adag E vet uy e from that of the beaches, and such northern 
forms as Modiola poenis and Cardium Mortoni, which are adapted to such extremes 
€f temperature, find here a congenial station. 
