84 ZOOLOG r. 



The tentacles next arise, being the elongation of the 

 cliambers between the partitions, six larger and elevated, 

 six smaller and depressed (Fig. 55, D). The definitive form 

 of the coral polyp is now assumed, and in the Astroides it 

 becomes a compound polypary. 



There are but few facts regarding the rate of growth of 

 corals. Pourtales states that a specimen of Mmandrina 

 laliyrintMca, measuring a foot in diameter and four inches 

 thick in the most convex part, was taken from a block of 

 concrete at Fort Jefferson, Tortugas, which had been in the 

 water only twenty years. Major E. B. Hunt calculated 

 that the average growth of a Ma?andrina obseived by him 

 at Key AVest was half an inch a year. From the observa- 

 tions and specimens collected by Mr. J. A. Whipple, as 

 stated by Verrill, a Madrepora found growing on the wreck 



of the Severn grew 

 a * to a lieight of sixteen 



feet in sixty-four 

 years, or at the rate 

 of three inches a 

 year. 



The group Rugosa 

 o f Milne-Edwards 



Fig. 50.— a. HaplophylUa paradoxa ; b. Ycrticiil eec- n-nrl TToimo r^nn + ni-no 

 tiou; c, cttlicle from above.— After Pourtalee. '^""^ -CXdime ooiiuaiiif) 



a large number of 

 palfeozoic corals, which are mainly characterized by septa 

 proceeding from four primary ones, the number in all liv- 

 ing corals being six ; and also by " the occurrence in them, 

 alone of all Atithozoa, of intracalicinal gemmation." 



Pourtales has doubtfully referred to this group his Haplo- 

 2}hyllia paradoxa (Fig. 56) which inhabits the Florida 

 Straits at a depth of over three hundred fathoms. The 

 nearest known fossil ally of this interesting coral is Oalo- 

 pliylhim profundum Germ., which is fossil in the Dyas for- 

 mation. Duncan describes Guynia annulcda, another deep- 

 sea coral, as a recent Eugose tetrameral coral. Moseley 

 suggests from a study of Heliopora, together with Orypto- 

 helia and other Stylasteridm, that ' ' the marked tetrameral 

 arrangement of the septa in Rugosa, and the presence in 



