1890.] NATURAL SCIKNCKS OF PHILADELPHIA. 311 



did not see a single starfish, nor were we more successful in uur 

 search after holothurians ; the latter animals are especially con- 

 spicuous on the corresponding sands of the liernnida Keefs. Far 

 otherwise was it among the growing heads of coral, although even 

 here the luxuriance of the Bermudas was wanting. The Diiulemn 

 setosa among sea-urchins was very plentiful, and we observed a num- 

 ber of large annelids, besides mollusks of various kinds. But the 

 bristling forest of millepores and sea-fans (gorgonians) was want- 

 ing, and with them the host of brilliantly colored foruis which live 

 in association. 



The water separating the reef-patches is of moderate (^le})th, but 

 at many points it descends below the 20-fathom line, or beyond 

 what is generally considered to mark the zone of living-reef struct- 

 nres. Thus, for most of the distance between the Isla Verde and Blan- 

 quilla (a little more than a mile and a half) the depth exceeds 100 

 feet, and at several places it varies from 120 to 130 feet; and 

 much the same depth is found between Blanquilla and Galleguilla 

 (one mile) and between the Isla Verde and the Islote de Pajaros (some- 

 Avliat over a mile). We frequently sounded in these greater depths, 

 and nowhere obtained positive indications of a coral growth ; the 

 greased lead invariably brought up sand particles, but no impres- 

 sions of either dead or living corals. I could not say positively, 

 however, that living coi'als may not be found in these deeper parts, 

 as our "grease" was perhaps a little too soft to retain distinct im- 

 pressions; but it is certain that wherever our sight penetrated the 

 perfectly crystal waters to a depth exceeding 80-35 feet it fell 

 on barren sand ; and I am not sure that we anywhere could see 

 living coral even at this depth. Usually the barren sands bounded 

 the reef-zone at a depth lying between 15 and 25 feet. 



The oceanic slope of the reefs is in most part a very moderate one, 

 but there are places where it is as much as 1 in 5 or even 1 in 4 

 (12-14 degrees). Of course, this is small in comparison with that 

 which is found in the case of many true atolls. Off the western 

 point of the Islote de Pajaros we obtained 75 feet at a distance of 

 little more than 200 feet from the breaking crest. As regards the 

 permanence in depth of the Avater-ways between the reefs it may 

 be said that many of our soundings corresponded absolutely with 

 the soundings registered in the Ponzoni map of 1807 (181G). This 

 correspondence was especially noticeable in the water-ways between 

 the Islote de Pajaros and the Isla Verde and between the latter and 



