MARINE PROVINCES. 55 
Buccinum. Velutina. *Crenella, 
*Chrysodomus. Lacuna. *Yoldia. 
*Trophon. *Margarita. *Astarte. 
Admete. —_— Cyprina. 
*Trichotropis. *Rhynchonella. Glycimeris. 
The following haye been thought peculiar to the warmer re- 
gions of the sea: 
Nautilus. Conus. Columbella. Perna. 
Rostellaria. Harpa. Cypreea. Vu'sella. 
Triton. Oliva. Nerita. Tridacna, 
Cancellaria. Voluta. Spondylus, Crassateila. 
Terebra. Margineila. Plicatula. Sanguinolar a. 
But it must not be inferred that these genera were always 
characteristic of extreme climates. On the contrary, the whole 
of them have existed in the British seas at no very remote geo- 
logical period. Lhynchonella and Astarte were formerly “‘ tropi- 
eal shells ;” and since the period of the English chalk-formation 
there have been living Nautili in the North Sea, and Cones and 
Olives in the ‘‘ London basin.” It is not true that the same 
species haye been at one time tropical, at another temperate, but 
the genera haye in many instances enjoyed a much wider range 
than they exhibit now. ‘Some of the ‘‘tropical” forms are 
more abundant and extend farther in the Southern hemisphere ; 
several large Volutes range to the extremity of South America, 
and the largest of all inhabits New Zealand. 
The tropical and sub-tropical provinces might be naturally 
erouped in three principal divisions, viz., the Atlantic, the 
Indo-Pacific, and the West-American,—divisions which are 
bounded by meridians of longitude, not by parallels of latitude. 
The Arctic province is comparatively small and exceptional ; 
and the three most southern Faunas of America, Africa, and 
Australia differ extremely, but not on account of climate. 
If only a small extent of sea-coast is examined, the character 
of its mollusca will be found to depend very much upon the 
nature of the shore, the tides, depth, and local circumstances, 
which will be referred to again in,another page. But these 
peculiarities will disappear when the survey is extended to a 
region sufficiently large to include every ordinary variety of 
condition. 
It has been stated that each Fauna consists of a number ot 
peculiar species, properly, more than half;’and of a smaller 
number which are common to some other provinces. By ascer- 
taining the direction of the tides and currents, and the circum- 
stances under which the species occur, it may be possible to 
determine to which proyince these more widely diffused mollusca’ 
