tS-i 



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 definitive form 

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

 becomes a compound polvparv. 



There are but few facts regarding the rate of growth of 

 corals. Pourtales states that a specimen of Mwandrina 

 libyrintliica, measuring afoot in diameter and four inches 

 tliick 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 ^Ifeandrina obseived 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 Yerrill, 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 

 of Milne-Edwards 

 and Haime contains 

 a large number of 

 palsozoic corals, which are mainly characterized bv having 

 four primary septa, the number in most living corals beins 

 six ; and also by intraculicinal gemmation, which also occurs 

 in a few Caiyophyllids and Ocuhnids. 



Pourtales has doubtfully referred to this group his Haph- 

 phyUia paradoxa {V\s,. 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- 

 pJii/Uum profnndum Germ., which is fossil in the Dyas for- 

 mation. Duncan describes Gitynia annulata, another deep- 

 sea coral, as a recent Rugose tetrameral coral. Moseley 

 suggests from a study of Heliopora, together with Crypto- 

 helia and other 8tylusterid(E, that " the marked tetrameral 

 arrangement of the septa in Rugosa, and the presence in 



Fis. 56. — a, BaplophyUia paradoxa ; 6. vortical seC' 

 -tion ; c. caJicle from .ibove, — After Pourtalee. 



