ZOOLOGY. 411 



with that of the Florida Bank, being characterized by the same 

 species of echinoderms,mollusks, crustaceans, corals, and fishes 

 already so well known from shallow water on the Florida side. 

 He also examined the great Alacran Reef. It resembles an 

 atoll in fall activity, the eastern slope being nearly perpen- 

 dicular, rising in a short distance from twenty fathoms to the 

 surface. "The whole structure of this reef shows its identi- 

 ty of formation with that of the main Florida Reef, and with 

 that of the reefs on the northern coast of Cuba, where the 

 line of distinct and powerful elevation can be still plainly 

 traced by old coral slopes, and by the ancient coral reefs in 

 the hills surrounding: Havana and extending; to Matanzas." 

 It is an atoll, Agassiz claims, apparently formed in areas of 

 elevation, though, according to Darwin's theory of the for- 

 mation of coral reefs, atolls could not be formed in areas of 

 elevation. Many interesting deep-sea forms were dredged, 

 and the Globigerina ooze, from 1323 fathoms upward, was 

 found to be rich in animal life. In 968 fathoms, specimens 

 of the eyeless macrouran (Willemoesia) were obtained, which 

 were identical, as were most of the deep-water species 

 dredged, with those brought up from great depths in the 

 Atlantic by the Challenger expedition ; a gigantic isopod, 

 more than eleven inches long, closely allied to JEga ; in 1568 

 fathoms, an UmbeUularia, and a transparent, brilliantly striped 

 holothurian were secured. From shallower water a number 

 of fine specimens of the extinct genus Conochjpus, of a brill- 

 iant lemon color, were dredged. 



Further dredgings were afterwards carried on by the same 

 party in the Florida Channel during March and April last- 

 Large numbers of Pentacrinus were obtained twenty perfect 

 specimens in all. The Marquesas Islands were found to have 

 been formed in the same manner as the great Alacran Reef 

 i. e., it is an atoll. It was found that the deep-water fau- 

 na on the western slope of the great Florida Bank corre- 

 sponds with that of similar depths on the eastern slope of 

 the Bank of Yucatan, and that this deep-water fauna extends 

 over the bottom of the Gulf of Mexico, until the line running 

 from the 100-fathom line in the latitude of Tampa Bay tow- 

 ards New Orleans strikes the Mississippi River slope. Here, 

 owing to the presence of dark, rich mud, the former was very 

 different ; while the hauls in still deeper water off the Mis- 



