MUSEUM OF COMPARATIVE ZOOLOGY. 365 



with a few small species of living corals, some Haleyonarians, and a 

 good many Alga?. From the nature of the bottom of this zone, espe- 

 cially at a depth of from twenty to forty fathoms, it is evident that a 

 large number of dead Mollusks and Zoophytes are scattered over its 

 surface by the agency of the currents and tides, after they have been 

 broken up. 



I do not now enumerate the particular animals and plants found 

 in this and the other submarine regions herein described, because the 

 work of identification is as yet very incomplete ; moreover, some of 

 the most common and characteristic species are as yet neither de- 

 scribed nor named, and would therefore be necessarily omitted in any 

 list of the characteristic species of the Gulf Stream fauna. Indeed, 

 for the present, such a list could only be an enumeration of species 

 with which naturalists have become acquainted from specimens cast 

 ashore, and would give no idea of the actual living fauna; in their 

 natural habitat. On that account it is particularly desirable that the 

 scientific harvest of these surveys should speedily be made known, 

 accompanied by the fullest illustrations* 



A third region or zone, beginning at a depth of about fifty or sixty 

 fathoms and extending to a depth of from two hundred to two hundred 

 and fifty fathoms, constitutes a broad slanting table-land, beyond which 

 the sea-bottom sinks abruptly into deeper waters. The floor of this 

 zone is rocky ; it is, in fact, a limestone conglomerate, a kind of luma- 

 chelle, composed entirely of the solid remains of organized beings, a 

 true concretionary limestone, such as we might find in several levels 

 of the Jurassic formation, and more especially in that horizon which 

 geologists call " Coral Rag." We have here a plateau extending for 

 more than a hundred miles, beginning off the Marquesas and stretch- 

 ing to Cape Florida, corresponding to Coral Rag. It varies from 

 eight to ten, twelve, or twenty miles in width, — the greatest spread 

 facing Sombrero, — and is built up entirely of animals now living 

 upon its surface, and constantly increasing the thickness of the bed 



* The corals found in the two earlier cruises are described by M. Pourtales, in Num- 

 bers 6 and 7 of the Bulletin, pp. 103-141. A preliminary report on the Echinoderms 

 is printed in Number 9 of the Bulletin, pp. 253- 361. As I have not enumerated the 

 species therein described, it may not be out of place here to remark, that, though I 

 have made some additions smce, this report was prepared before Numbers 9, 10, 11, 

 and 12 of the Bulletin had been handed in. The remarks upon the growth of corals 

 were written immediately after my return from Florida, in May last. 



