84 



ZOOLOGY. 



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 definitiTe 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 

 labyrintMca, measuring a foot in diameter and four inches 

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

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

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

 that the average growth of a Mseandrina obsei-ved 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 Jieight of sixteen 

 feet in sixty-four 

 years, or at the rate 

 of three inches a 

 year. 



The group Rugosa 

 o f Milne-Edwards 

 and Haime contains 

 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 Oculiuids. 



Pourtales has doubtfully referred to this group his Haplo- 

 phyllia 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- 

 phyllum profunduni Germ., which is fossil in the Dyas for- 

 mation. Duncan describes Guynia annulata, another deep- 

 sea coral, as a recent Kugose tetrameral coral. Moseley 

 suggests from a study of Beliopora, together with Grypto- 

 helia and other Sfylasterida, that " the marked tetrameral 

 arrangement of the septa in Rugosa, and the presence in 



Fig. 56.^-70, SaplophyUia paradoxa ; b. verdcal sec 

 tion; <;, calicle from above.— After Pourtales. 



