132 



THE VOYAGE OF H.M.S. CHALLENGER. 



and the genus Leptopenus, which has as yet been dredged only south of the equator, 

 but both in the South Atlantic, South Indian, and South Pacific Oceans in very great 

 depths. 



No examples of any of the species of the genus Stephanotrochus were obtained in 

 the Pacific Ocean They have hitherto occurred only in the Atlantic and South Indian 

 Oceans. I have taken care to give in the description of the figures at the end of this 

 memoir the exact locality at which each specimen figured was dredged, because local 

 varieties may at some future time be determined, and, moreover, forms placed and named 

 together may hereafter be separated. 



The wide range in depth of some species is very remarkable, and the instance of Bathy- 

 actis symmetrica has often been referred to since the Challenger Expedition returned ; it 

 ranges from a depth of 70 fathoms in the tropics to one of 2900 fathoms. The following 

 table gives the depths at which all genera of corals which have as yet been found at a 

 depth of 50 fathoms and upwards occur. The occurrence of the genera as fossils in 

 Secondary and Tertiary deposits is also indicated. Some shallow water forms extend to 

 very considerable depths. The deep-sea forms are not as a whole of greater geological 

 antiquity than shallow water forms. 



Table showing the Depths at rohich all Genera of Corals, which have as yet been 

 obtained in Depths of 50 Fathoms and upwards, are known to occur. 



The depths are given in round numbers, and the x 's indicating the ranges of the coral in depth are placed 

 in those columns the numbers relating to which approach most nearly to the depths at which the corals 

 have been actually dredged. Thus, if a coral has been dredged at 76 fathoms, it is marked in the 100 

 fathoms' column; if at 74, in the 50 fathoms' column; if at 1126, in the 1250 column; if at 1124, in 

 that of 1000 fathoms. 



