. 
THE ; CONCHOLOGISTS’ - EXCHANGE. 51 
it lives in fresh water or that which is more or 
less salty, and N. lineolata, and macrastoma, 
which I found in Honduras in the mouths of 
rivers often extended into the sea. Planorbis 
tumidus was often found in slightly brackish 
water in Florida, and the [imnzas in the Bal- 
tic, and some places on the British coasts mingle 
with the Littorinas. 
Ampullaria caliginosa, a Mexican species, 
closely related to A depressa,if not identical 
with it, Planorbus tumidus, and Havanensis,* 
and a few other tropical species found to-day in 
the Southern States, may have been introduced, 
I think, in the manner of which I have spoken. 
Of course such voyages of living snails, with a 
successful termination, could only happen 
rarely, but it must be remembered that countless 
ages have elapsed since the present species have | 
occupied the earth. Of the 180 species of 
trees found in the State of Florida, fully one- 
third are natives of the West Indies or the 
American tropics, besides great numbers of 
shrubs and herbaceous plants, Of her ten or 
a dozen palms, nearly all are West Indian. 
The Royal Palm is found in South Florida, and 
growing on it the Dendrophylax, Lindeni, a | 
lovely orchis that I have seen on it in Utilla, 
both probably having made the voyage together, 
as I believe it grows on no other tree. If then 
a host of plants and trees from the tropics, 
among them a number of ferns and Epiphytal 
orchids of the tenderest character, and whose 
seeds would undoubtedly be destroyed by long | 
contact with salt water, have drifted across and 
become established in Florida, I do not see why 
afew land and fresh water species of shells 
might not do the same thing; and I should not 
be surprised if future and more careful search 
in the almost impenetrable wilds of South 
Florida would bring to light a large number of 
West Indian Land and Fresh-water mollusks. 
Certainly in this case it cannot be claimed 
that Florida has been connected with the Island 
of Cuba, the Bahamas, or any of the West In- 
dies in recent times, as the State has been up- 
heaved from the sea since the commencement 
of the tertiary epoch, and within the time of 
the present species has increased its area at the 
southern extremity by means of the corals. 
*Tdentified by Mr H.-A. Pilsby, who has madea 
special study of the genus Planorbis. 
Nor do I think the theory is reasonable that 
many of these shells have passed around into 
‘Florida from Mexico by way of the southern 
shores of the Gulf States. Within a compara- 
tively limited time the land near the mouth of the 
Mississippi has been deposited by that stream, 
fillmg up a shallow estuary that extended far 
up the valley into a region too cold for most of 
these species to have survived in; besides, 
most of these tropical shells are not found in 
this regior? to-day, but in the southernmost part 
of Florida. Neither is it probable that they 
were brought there through the agency of 
man, as Southern Florida is an almost uninhab- 
ited wilderness, and has been so since the com- 
mencement of its history. I have spoken in this 
article, of shells being introduced into Florida, 
because I am most familiar with it and its shell 
fauna, but numbers of similar instances could 
be given all over the tropics. 
Ogallala, Neb., Aug. 8, 1887. 
Concluded, 
ON A NEW FLORIDIAN NATICA. 
NATICA FORDIANA, N. S. 
Shell small, conic globose, white and shin- 
ing throughout ; whorls well rounded, plicately 
striate below the suture, where they are encir- 
cled by about six faint lineal sulcations, giving 
the spire and upper part of the body whorl a 
slightly decussated appearance ; suture well im- 
pressed, umbilicus open, bounded by a slight 
groove; columella only slightly callously thick- 
ened; operculum corneous. Length, 40 inches, 
diameter, 30 inches. Some twenty or more 
specimens of this fine little species were taken 
alive on sand flats in Sarasota Bay, Florida, by. 
the writer, during a severe norther ina locality 
only laid bare ty the heaviest storms, I had 
supposed it to be a form of A. semsulcata, 
Gray. This latter species is placed in the sec- 
tion Stignzaulax of the typical Naticas, a section 
with grooved whorls, but Mr, Tryon states 
that he had never seen the operculum of 4. 
semisulcata, and thought that it might possibly 
be a amma. My friend, Mr. John Ford, of 
the Acad. Nat. Sciences of Philadelphia, hav- 
