146 BULLETIN ; MUSEUM OF COMPARATIVE ZOOLOGY 



of Santa Cruz we have horseshoe-shaped reefs following the outline of 

 the banks at depths of from six to ten fathoms. In the majority of these 

 cases we might look upon these curved reefs as atolls. They vary greatly 

 in outline, following closely the depths at which they best thrive, and 

 have usually taken from the shape of the basis upon which they have 

 developed the outline of a more or less circular belt. The summits 

 which have risen above the sea level are many of them more or legs 

 circular or irregularly elliptical, like St. Vincent, Grenada, and Domin- 

 ica. Others are greatly indented, like the Grenadines, Martinique, 

 Guadeloupe, and St. Martin ; while among the northern islands we find, 

 as among the smaller Grenadines, many irregularly shaped islands, as 

 Santa Cruz, Anguilla, St. Thomas, Cat Island, and the like, along the 

 shores of which we also find lines of irregular, broken reefs. 



The 100 fathom line of the banks on the west face of the Windward 

 Islands is comparatively close to the shore, the sea face is quite abrupt, 

 and the mass of volcanic mud and other material which is washed down 

 during the rainy season is quite sufficient to prevent the growth of frin- 

 ging reefs, which are so flourishing on the weather side. Were the banks 

 of the Windward Islands fringed only by low, narrow islands, like the 

 Bahama Banks, we might expect to find reefs growing on their western 

 edge, forming thus a number of atoll-like banks, such as Crooked Island, 

 Caicos, and Hogsty Reef. 



Horseshoe-shaped or semicircular reefs exist on isolated banks in the 

 Caribbean, as for instance on the Morant Cays, Serranilla, Serrana, and 

 Quita Sueno Banks. There are also curved reefs simulating semi-atolls 

 on the Mosquito and Yucatan Banks, such as Edinburgh Reef, Half- 

 Moon Reef, and the Hobbies on the former, and the Triangles, Sisal, and 

 Cay Arenas Reefs on the latter, besides the Alacran atoll. 



Finally, off Belize we have the isolated banks of Chinchorro, Turneffe, 

 Lighthouse Reef, and Glover Bank, all more or less irregularly elliptical, 

 and rising from deep water beyond the 100 fathom line and inside the 

 five hundred fathom limit, the east face of the last running rapidly into a 

 depth of one thousand fathoms, while the slope of the Chinchorro Bank is 

 comparatively less steep, the 1,000 fathom line being at least twenty-five 

 miles to the eastward. Nearly the whole length of the coast off" Belize, 

 from Ambergris Point to Cape Three Points, is protected by a reef which 

 lines the edge of the bank inside of Turneff'e Island. 



Let us now examine the banks of the Windward Islands formed by the 

 100 fathom line and compare them with the Banks of the Bahamas. 



Beginning with the Grenadines Bank and throwing out of account the 



