84 ZOOLOO Y. 



The tentacles next arise, being the elongation of the 

 chambers 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 Mceandrina 

 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 Maeandrina observed by him 

 at Key West 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 

 to a height of sixteen 

 feet in sixty-four 

 years, or at the rate 

 of three inches a 

 year. 



The group Rugosa 

 o f Milne-Edwards 



Fig. 56. a, Haplophyllia paradoxa ; b. vertical sec- n-n/1 TTaimp pnnt'iirii? 

 tionf e, calicle from 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 Haplo- 

 pJiyllia paradoxa (Fig. 56) which inhabits the Florida 

 Straits at a depth of over three hundred fathoms. The 

 nearest known fossil a'ly of this interesting coral is Calo- 

 phyllum 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 Stylasteridce, that " the marked tetrameral 

 arrangement of the septa in Rugosa, and the presence in 



