No. 2. — On the Rate of Growth of Corals. By Alexander 



Agassiz. 



We know as yet comparatively little regarding the rate of growth of 

 corals under different conditions. Dana has given, in his " Corals and 

 Coral Islands," * a resume of our knowledge on the subject, so that it 

 is only necessary for me here to refer the reader to his account of the 

 statements of Darwin, Stuchbury, Duchassaing, Verrill, and others, re- 

 lating to this subject. 



The specimens figured in this communication have been kindly sent 

 me by Lieut. J. F. Moser, commanding the U. S. Coast and Geodetic 

 Survey steamer "Bache." They were all taken (as stated by Mr. 

 Hellings, the cable manager) off the cable laid between Havana and 

 Key West, in June, 1888, from a portion of the cable repaired in the 

 summer of 1881 ; so that the growth is about seven years. Lieutenant 

 Moser writes : " Taken from the shore end of the International Cable ; 

 the specimens were taken between the triangular buoys and the outer 

 reef, the shore end being that portion between Key West and the outer 

 reef." The Coast Survey maps indicate a depth of from six to seven 

 fathoms, and this portion of the cable is most favorably situated as re- 

 gards food supply, being directly in the track of the main flow of the 

 tide as it sweeps in and out from the outer reef into Key West Harbor, 

 and over the flats to the northward. 



Some of the specimens belong to different species from those of which 

 the rate of growth was already known. 



Orbicella annularis (Plates I. and II.) shows a much greater increase 

 in the thickness of coral formed than the case mentioned by Verrill, 

 where the thickness formed in sixty-four years was not more than 

 about eight inches. The specimens sent by Lieutenant Moser grew 

 to a thickness of two and a half inches in about seven years. 



* Coral and Coral Islands, by James D. Dana. Third edition. New York, 

 1890. (Pp. 123, 253, 418 ) 



VOL. XX. — NO. 2. 



