84 ZOOLOG Y. 



The tentacles next arise, being the elongation of the 

 chambers between the partitions, six larger and elevated, 

 six smaller and depressed (Fig. 55, I)). 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 Mceandri/m 

 labyrinthica, 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 observed 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 



fl to a height of sixteen 



feet in sixty-four 

 years, or at the rate 

 of three inches a 



year. 



jf \3RJHf The 



^"^ of Milne-Edwards 



Fig. 56. a. Haplophyllia paratlora ; b vertical sec- an( J Haime Contains 

 tion; c, caliclefrom above. After Pourtales. 



a large number of 



palaeozoic corals, which are mainly characterized by having 

 four primary septa, the number in most living corals being 

 six ; and also by intracalicinal gemmation, which also occurs 

 in a few Caryophyllids and Oculmids. 



Pourtales has doubtfully referred to this group his Hapln- 

 pliyttia 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 Calo- 

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

 mation. Duncan describes Guynia annulata, another deep- 

 sea coral, as a recent Rugose tetrameral coral. Moseley 

 suggests from a study of Heliopora, together with Crypto- 

 lielia and other Stylasteridcs, that " the marked tetrameral 

 arrangement of the septa in Ruyosa, and the presence in 



