MUSEUM OF COMPARATIVE ZOOLOGY. 3 



of corals identical with those now found on the living reefs. Alacrau 

 Reef thus gives us an easy explanation of atols, apparently formed in 

 areas of elevation, and I shall on another o(Jcasiou further compare the 

 structure of this interesting reef with that of the great Florida Reef, and 

 of the Bahamas Bank, as I look upon it as a sort of epitome of the mode of 

 formation of these extensive reefs. Taken in connection with its position 

 on the Yucatan Bank, it will perhaps explain the mode of formation of the 

 greater part of the Florida peninsula as connected with the bank lying to 

 the westward of the mainland and to the northward of the Florida Reefs. 



Along the Cuban coast the dredge brought up a large number of si- 

 licious sponges, as well as many interesting forms of Corallispongia). 

 Here we found a species of Favosites, perhaps the most interesting coral 

 ever dredged, and many of the corals and Gorgonise collected by Count 

 Pourtalus on the rocky plateau to the south of the Florida reefs in from 

 200 to 300 fathoms. Although innumerable fragments of stems of 

 Pentaci-inus and portions of the arms frequently came up in the dredge, 

 we were not fortunate enough to obtain a single entire specimen, but we 

 obtained a young Holopus in excellent condition. While running our 

 first line from Havana to Key West, we used the dredge exclusively, 

 and brought up from the trough of the Gulf Stream in the deepest parts 

 nothing but Globigerina ooze, apparently confirming Mr. Pourtales's 

 results, who, in 500 fathoms' dredging over the same kind of bottom, 

 had also found nothing indicating an abundant fiiuna. 



Subsequently, however, we used the trawl and a modification of the 

 dredge over the same bottom, on the line from Cape San Antonio to 

 Sand Key, and we were surprised to find an abundance of life at all 

 depths, from 1,323 fathoms upwards, showing that the Globigerina ooze 

 is, on the contrary, particularly rich in animal life, as Thomson and his 

 associates in the " Challenger " also found it to be. Our hauls over this 

 Globigerina ooze and coral ooze gave us Echinoderms, Hydroids, Polyps, 

 MoUusks, Crustacea, Annelids, and Fishes ; one of the most interesting 

 hauls on this line was from 8G0 fathoms, bringing up an unusually large 

 number of Lamellibi-anchiata and Gasteropoda of small size, but includ- 

 ing many of exquisite beauty. 



The results of the hauls on the line from the Tortugas to the eastern 

 edge of the Yucatan Bank were perhaps the most interesting, and I had 

 often occasion, while examining the contents of the trawl from our 

 greatest depths to recognize old " Challenger " friends, — forms I had bo- 

 come acquainted with while examining the collection of the " Challenger " 

 last winter in company witli Sir Wyville Thomson. 



