Bland.] ^ * [March 3, 



Section IV. Punto Bico with Vieque, the Virgin Islands, Sombrero, 

 Anguilla, St. Martin, St. Bartholomew, and St. Croix. 



Puerto Rico, Yieque and the Virgin Islands, of which Anegada is the 

 most eastern, stand on one and the same bank, an elevation of -whieh to 

 the extent of somewhat less than 40 fathoms (240 feet) would unite the 

 whole, converting them into one Island. Sombrero is on another bank, 

 about 40 miles from the Virgin bank, and 23 miles from the north end of 

 the Anguilla bank. The depth of the channels which separate the Som- 

 brero bank from the Virgin bank on the west, and the northern end of the 

 Anguilla bank to the east, is not known, but soundings are recorded, at 

 their margins, of 160 fathoms (9G0 feet} and 190 fathoms (1,140 feet), with- 

 out bottom. 



Anguilla, St. Martin and St. Bartholomew stand on the western edge 

 of another bank of considerable extent. Its southeastern end is 14 miles 

 only from the Antigua bank, and the depth of water between the two is 

 upwards of 122 fathoms (732 feet). An elevation of the Anguilla bank of 

 about 40 fathoms (240 feet) would unite the Islands upon it. 



The land shell fauna of the above named Islands is unquestionably the 

 same ; it has some alliance with that of Haiti, but very little with that of 

 the Islands to the south of the Anguilla bank. Not only is the absence 

 of certain genera prevailing in Sections I., 11. , and III. noticeable, tut 

 the diminished number of representatives of others is equally so, for 

 example : 



in§I. §111. §IV. 



Megalomastoma 13 species, 1 3 



Aleadia 9 ^' 2 1 



Strophia 27 '' 2 2 



]\[acroceramus .35 " 10 2 



Cyliudrella 93 " 28 C 



The fact t\\2it Megalomastoma, Aleadia, Strophia, and Macroceramus are 

 not represented in the Islands south of the Anguilla bank (§ V.) and that 

 in those Islands there are 4 species only of Cylindrella, atfords striking 

 proof of the difference of their faunas. 



St. Croix is not unfrequently classed with the Virgin Islands, from 

 which it is 35 miles distant, but it stands on a bank disconnected from 

 any others and with very deep water around it. Soundings are on record 

 (taken, I believe, by Capt. Parsons, R. N,), between it and the Virgin 

 bank, about the mid-channel, of 1,050 fathoms (9,300 feet), and not far 

 from its northern shore of 2,000 fathoms (12,000 feet), without bottom being 

 found. 



The following soundings to the eastward were obtained by the U. S. 

 S. Yantic, in 1870, between St. Thomas and Saba : 



fathoms, feet. 



K Lat. 180 01' 50". W. Long. 64o 10' 20".— 1,825 = 10,950 



170 55' 00". '' 630 50' 30".— 1,240 = 7,440 



