MUSEUM OF COMPARATIVE ZOOLOGY. 123 



This region ceases at a depth varying from 250 to 350 fathoms ; the 

 third region begins with a more rapid slope, and extends over the whole 

 trough of the channel, the depth of which in this part does not much 

 exceed 500 fathoms. This is the great bed of Foraminifera, and more 

 specially of Globigerinre, which covers so great an extent of the bottom 

 of the ocean, and which, as we shall see, is not destitute of living rep- 

 resentatives of the higher branches of the animal kingdom. 



The Fauna of the three regions is very distinctly marked. The first 

 region is singularly barren, and shows that the rich Fauna of the 

 Florida reef extends but very little to seaward or into depth. The 

 greater number of the shells brought up are dead and broken, and can 

 scarcely be regarded as characteristic, as large numbers of them have 

 evidently served as food for turtles and fishes, and may have been thus 

 transported some distance. Crustaceans and Annelids are more com- 

 mon. The Echinoderms are represented by a fnw Ophiurians, and the 

 Corals chiefly by Balanophyllia floridana, nov. sp., very abundant in 

 some places, particularly near Sand Key. 



The second region, on the contrary, is remarkably rich in animal 

 forms, which may be in part attributed to the hard aud rough bottom 

 offering points of attachment and shelter. If this formation were 

 emerged, the geologist would find it to consist of beds of limestone 

 full of fossils, of which we shall point out the most characteristic ones ; 

 remarking, however that though the great majority of the animals fur- 

 nishing those remains now live on the bottom, a i'tw contribute by 

 sinking after death from the higher regions of the superincumbent 

 water (teeth of fishes and shells of Pteropods), and others are brought 

 by currents from littoral regions (bones of Manatee, fragments of 

 littoral plant-). 



The Vertebrates are represented by the bones of the Manatee, chiefly 

 fragments of the ribs. These are quite abundant, no less than ten or 

 twelve casts of the dredge having brought them up, generally several 

 pieces at a cast. Until we are better acquainted with the set of the 

 currents on the west coast of Florida and the coast of Cuba, the former 

 habitat of these animals cannot be guessed at with much certainty, 

 as their carcasses, either floated out of the estuaries of those coasts, or 

 when very numerous, as they evidently were, the animals may have 

 been in the habit of migrating across the straits, and may have been fre- 

 quently destroyed by sharks on the passage. As no fresh addition of 



