114 CORALS AND CORAL LSLAND8. 



cies ; and Millepora alcicornis is an identical species, though 

 different in variety. 



The Bermudas are in the North Atlantic subtorrid region, 

 in the range of the Gulf Stream. The few reef-making species 

 that occur there are all West Indian, viz. : The species of the 

 Astreea tribe, Isophyllia dipsacea, I. rigida, Diploria cerebri- 

 formis; of the Oculina tribe, Oculina diffusa, Oculina varicosa, 

 Oculina pattens, Oculina Valenciennesii ; of the Fungia tribe, 

 Siderastrcea radians, Mycedium fragile ; of the Madrepora 

 tribe, Parties clavaria ; also the Millepora alcicornis, and the 

 common West India Alcyonoids, Gorgonia Jlabellum, Plexaura 

 crassa Lx., PL fiexuosa Lx., PL homomalla Lx., Pterogorgia 

 Americana Ehr., Pt. acerosa, Ehr. 



The facts presented are sufficient to show that temperature 

 has much to do Avith the distribution of reef-corals in latitude, 

 while proving also that regional peculiarities exist that are not 

 thus accounted for. 



II. DISTRIBUTION IN DEPTH. 



Quoy and Gaymard were the first authors who ascertained 

 that reef-forming corals were confined to small depths, contrary 

 to the account of Foster and the early navigators. The mis- 

 take of previous voyagers was a natural one, for coral reefs 

 were proved to stand in an unfathomable ocean ; yet it was 

 from the first a mere opinion, as the fact of corals growing at 

 such depths had never been ascertained. The few species which 

 are met with in deep waters appear to be sparsely scattered, 

 and nowhere form accumulations or beds. 



The above-mentioned authors, who explored the Pacific in 

 the Uranie under D'Urville (and afterward also in the As- 

 trolabe), concluded from their observations that five or six 

 fathoms (30 or 36 feet) limited their downward distribution. 



