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 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 Meandrina 
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 Meandrina 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 
of Milne-Edwards 
Fig. 56.—a, Haplophyllia paradoma ; b. vertical sec- 1 M 
tlont’c, calicie from above,—After Pourtales, and Haime contains 
a large number of 
palzozoic 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 Oculinids, 
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 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- 
helia and other Stylasteride, that ‘‘ the marked tetrameral 
arrangement of the septa in Rugosa, and the presence in 
