60 
Bland.] 
March 8, 
fathoms (2,316 feet), while the maximum depth known, as above stated, 
between Tobago and Barbados, is 1,060 fathoms (6,360 feet). 
It appears from the foregoing evidence, that Trinidad, Tobago, the 
Grenada bank (an elevation of which to the extent of 40 fathoms would 
give an Island nearly 100 miles in length), and St. Vincent, stand on a 
partially submerged ridge, an extension of the South American Continent, 
having, say, 1,000 fathoms depth of water on the west side, and still greater 
depths between its northern termination and St. Lucia, also ouits eastern 
side between it and Barbados, and between the latter Island and Tobago. 
The summit of this ridge is 2,316 feet beneath the level of the sea be- 
tween Trinidad and the Grenada bank, and, say, 1,800 feet between that 
and St. Vincent, while the altitudes above the sea are, of Trinidad 8,100, 
Tobago 1,800, Grenada 2,746, and St. Vincent about 3,000 feet. 
The genera and species of land Mollusks which occur in the Islands on 
the “submerged ridge” just mentioned (Trinidad to St. Lucia inclusive), 
are chiefly allied to those which are characteristic of Venezuela, the por- 
tion of the Continent contiguous to Trinidad. The species of Seitz, 
in its wide application, including Stenopus, Hyalina, and Zonites, are 15 
only in number, while there are of Bulémus (as restricted by Albers) 5, and 
of Pulimulus 14 species, the total number of species of the latter in the 
West Indies, being about 38. The subgenus Dentellaria (Helix) is character- 
istic of the Islands embraced in Subdivision 1 of Section V., but has few 
representatives in those named in Subdivision 2. D. perplexa, Fer., is 
peculiar to the Grenadines and Grenada, D. Isabella, Fer., is common to 
one of the Grenadines, Barbados, and Cayenne, (French Guiana,) and D. 
orbiculata, Fer., toSt. Lucia, Martinique and Cayenne. 
The genus Bulimus, of which the subgenera represented are Borus, 
Pelécychilus, and Hurytus, all South American, occurs in the West: Indies 
only in the group (subdivision 2) embracing St. Lucia and Trinidad and the 
intermediate Islands. Borus oblongus inhabits Barbados, but it was 
introduced there from St. Vincent by the late Rev. Mr. Parkinson. 
Hurytus aulacostylus, Pf., occurs both in St. Lucia and Demerara. 
With respect to Trinidad, it is certainly curious that we have there a 
species of Diplommatina (D. Huttoni, Pf.) and of Ennea (#4. bicolor, 
Hutton). the latter found also in Grenada and St. Thomas, both living in 
the East Indies. Guppy has lately discovered a species to which he has 
given the generic name of Blandiella, but it is, I think, a Truncatella, 
allied, at least, to the subgenus Taheitia, H. and A. Adams, the type of 
which is 7. porrecta, Gould, of Taheiti. 
The land shell fauna of the Islands in subdivision 2 have marked alliance 
with that of Cayenne. There are on that group six species of Helix which 
are also found in Cayenne, viz.: Dentellaria orbiculata, nua-denticulata, 
dentiens, Isabella, badia, and Thelidomus discolor. The genus Cyclophorus 
has no less than seven species in Martinique, Dominica, and Guadeloupe, 
but none in any other part of the West Indies, while one, a different 
species, inhabits Cayenne. In Barbados no member of the family 
Cyclostomacea has been discovered. I have already referred to some 
other peculiarities of this fauna as compared with that of the Islands 
