1871.] "^ [Olaiul. 



fathoms (2,31G feet), while the maximum depth known, as above stated, 

 between Tobago and Barbados, is 1,000 fathoms (6,860 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, andstill greater 

 depths between its northern termination and St. Lucia, also on its eastern 

 side between it and Barbados, and between the latter Island and Tobago. 

 The summit of this ridge is 3,316 feet beneath the level of the sea be- 

 tween Trinidad and the Grenada bank, and, say, 1,800 feet between that 

 and St. Yincent, while the altitudes above the sea are, of Trinidad 3,100, 

 Tobago 1,800, Grenada 2,746, and St. Vincent about 3,000 feet. 



The genera and species of land IMollusks 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 Helix, 

 in its wide application, including Stenopus, HyccUna, and Zonites, are 15 

 only in number, while there are of BuUmus (as restricted by Albers) 5, and 

 of Bulimulus 14 species, the total number of species of the latter in the 

 Westlndies,being about 38. The subgenus Dentellaria {Eelix) is character- 

 istic of the Islands embraced in Subdivision 1 of Section V., but has few 

 representatives in those named in Subdivision 2. D. perpUxa, Fer., is 

 peculiar to the Grenadines and Grenada, D. Isabella, Fer., is common to 

 one of the Grenadines, Barbados, and Cayenne, (French Guiana,) and I). 

 orhiculata, Fer., to St. Lucia, Martinique and Cayenne. 



The genus BuUmus, of which the subgenera represented are Borus, 

 PelecycMlus, and Eurytus, all South ximerican, occurs in the West Indies 

 only in the group (subdivision 2) embracing St. Lucia and Trinidad and the 

 intermediate Islands. Borus oUongus inhabits Barbados, but it was 

 introduced there from St. Vincent by the late Rev. Mr. Parkinson. 

 Eurytus aulacoslylus, Pf., occurs both in St. Lucia and Demerara. 

 AYitli respect to Trinidad, it is certainly curious that we have there a 

 species of Diplo^mnatina (D. Huitoni, Pf.) and of Ennea [E. picolor, 

 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 subgeaus Taheitia, H. and A. Adams, the type of 

 which is T. 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 orhiculata, nux-denticulata, 

 dentiens, Isabella, badia, and Thelidomus discolor. The genus Gyclophorus 

 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 comjpared with that of the Islands 



