THE STRUCTURE OP PORITES. 491 



These secondary coenenchymatous developments have given 

 rise to some confusion, their morphology not being always clear, 

 especially when the calicles are crowded and the ridges appear 

 as mere upward extensions of the walls. In the ' Challenger ' 

 Eej)ort on the Eeef Corals (xvi., 1886), two new forms, P. crassa 

 and P. latistellata, Quelch, are described ; but, according to the 

 classification there adopted, they should have been placed in the 

 genus Synarcea^ which was established to contain all the Poritid 

 forms with ridges or papillae rising from the walls between the 

 calicles. P. latistellata was so named because the individual 

 calicles were measured as if these secondary coenenchymatous 

 ridges were the tops of the walls ; and in an allied form, where 

 the ridges ran so as to separate the calicles into short linear 

 series in the bottoms of narrow valleys, such series were thought 

 to be the result of intracaliciaal gemmation. This led Mr. Quelch 

 to found a new genus, Napopora. Eecent acquisitions by the 

 British Museum have supplied us with links sufficient to connect 

 the types of the new genus specifically with P. latistellata. 



A few of these different types of wall will be seen in Plate 35. 

 Representatives of the two extremes can be seen and compared 

 in figs. 5 and 6. How impossible it is to make generic distinctions 

 between them, may be gathered from the fact that specimens 

 occur in which part of the stock has walls even thinner than 

 those shown in fig. 5 ; while another part of the same stock has 

 walls as thick as those shown in fig. 6, although without the 

 special coenenchymatous papillae. 



The finer texture of the walls can be best discussed in con- 

 nection with the septa. 



The Sejpta. — The number usually assigned to Porites is twelve, 

 and it seems quite possible to separate Porites from Goniopora 

 mainly on this point, Goniopora liaving typically 24. Dr. Verrill 

 ascribed " 12, sometimes 12 to 20, rarely 24 " septa to Porites ; 

 but I have found it better to class every Poritid with more than 

 12 septa in the genus Goniopora, as Dana proposed. Mr. Quelch, 

 again, claimed 24 septa for Porites (Chall. Eep. xvi.), on account 

 of his species P. mirabilis, in which calicles occur with 3 cycles 

 of septa. These, however, are obviously the large double calicles, 

 one or two of which can be found on almost any stock and 

 must be regarded as abnormalities. One is seen in fig. 5, 

 PI. 35. 



"With regard to the development of the septa in Porites 



