368 AMERICAN JOURNAL 



III. Western Caribbean Islands (most Leeward, and in- 



cluding some of the Windward islands), viz. : Vir- 

 gin Islands, St. Kitts, Nevis, Montserrat, Dominica, 

 St. Lucia, St. Vincent, Grenada and Grenadillos. 



IV. Eastern Caribbean Islands (most Windward, and some 



Leeward islands), viz : Anguilla, Barbuda, An- 

 tigua, Barbados and Tobago. 

 V. Trinidad. 



It will be noticed that the Virgin Islands and Anguilla, em- 

 braced, with islands to which by their land-shell faunas they 

 are closely allied, in my Porto Rico subprovince, are placed 

 by Grisebach, the former in his third, and the latter in his 

 fourth section, and both with islands, to which they are not so 

 allied, comprised in my Guadeloupe subprovince. 



The boundaries (shown by the distribution of the land shells) 

 of the Porto Rico and Guadeloupe subprovinces are somewhat 

 sharply defined, and, in connection with an explanation as to 

 their limits, there are some facts (for which I am indebted to 

 Mr. Julien) relating to the geological position of part of the 

 former subprovince, which deserve consideration. 



The Eastern portion of the Porto Rico subprovince consists 

 of the Virgin and St. Martin banks and the Key of Sombrero, 

 the latter dividing the channel between the banks into two 

 passages, — the Anegada on the west, and the Sombrero passage 

 on the east of the Key. The Virgin bank, the nearest point 

 of which is forty miles from the Key, encircles St. Thomas, 

 St. John, Tortola, Anegada and the other islets of the Virgin 

 group, — deep water soundings oft' the edge of this bank vdvy 

 from 140 to 160 fathoms. I'he Key of Sombrero is also sur- 

 rounded by a submarine bank, the dimensions of which are 

 about three and a half by five miles, — soundings off" the outer 

 edge give from 105 to 150 fathoms. The St. Martin bank, 

 south-east of and about twenty miles from the Key, comprises 

 the islands of Anguilla, St. Martin and St. Bartholomew ; 

 soundings oft' tlie edge of the bank vary from 102 to I'JO 

 fathoms. 



The northern part of the Guadeloupe subprovince consists 

 of the islands immediately south and east of the St. Martin 

 bank, viz.: St. Kitts, Barbuda and Antigua, with the smaller 

 islanls of St. Eustatius and Nevis. 



The following are the principal dift'erences in the distribu- 

 tion of genera and species of land shells, on whic'i I rely as 

 authority for separating the last mentioned islands from the 

 Porto Rico subprovince, and placing them, with the islands to 

 the south, in the Guadeloupe subprovince: — 



Megalomastoma and Alcadia are found in Porto Rico, also 



