14 MADREPORARIA. 



not be considered to be of any value as morphological units. Goniopora and Porites were the 

 two genera of the Poritidae and deducible from Madreporids ; Porites being the primitive 

 form and Goniopora to be derived from Porites by simple enlargement. At the same time 

 Dana's suggestion (see above, p. 11) is quoted that the genera may be parallel and analogous 

 off-shoots from different ancestral forms. 



In the following pages it will be shown that Goniopora is the more primitive, 

 and that Porites can be deduced from it by a simple process of reduction of its septal 

 formula. 



In the foregoing historical sketch of our knowledge of the genus Goniopora, no fossil forms 

 have been recorded. This was one of the reasons which led me to think that the genus was 

 more recent and even a possible derivative of Porites. As a matter of fact, the large and 

 important group called " Litharcea" consists solely of fossil Goniopores. The distinction drawn 

 by Milne-Edwards and Haime between Litharcea and Goniopora was based upon insufficient 

 material. 



(6) Litharasa M.-E. & H. 



This genus was founded in 1850 by Milne-Edwards and Haime, * for a Poritid found in 

 great numbers at Bracklesham Bay, Sussex, and first described and figured by Bowerbank in 

 1840 1 as an Astraeid (" Astrea Websteri "). 



In the same year as the genus was founded, Lonsdale % described it as a Siderastrcea 

 (S. Websteri). 



It was diagnosed by Milne-Edwards and Haime as differing from Goniopora in the fact 

 that its septa were not so " trabecular," and in this respect, viz. in the possession of more 

 completely solid septa, it was thought to approach the Astrseids. It accordingly occupied in 

 their system one extreme of the Poritidse, while Alveopora with its spinous septal ingrowths 

 occupied the other. On the supposed absence of the pali, see p. 146. 



This arrangement is purely artificial. Genera cannot of course be founded on characters 

 which differ only in degree. A generic character must express some essential difference of 

 structure, and any such difference between Goniopora and Litharcea, I have failed entirely to 

 find. 



Since 1850 many fossil Gonioporas have been described as Litharcea or Porites. The 

 dictum of Milne-Edwards and Haime that Goniopora was a recent form, seems to have been 

 blindly followed, for no suggestion seems to have been made that the very porous septa of 

 some of these Litharceas constituted them true Gonioporce. 



That many of them should have been classed as Porites is due to the fact that the 



* Brit. foss. Corals, p. 38, pi. vi. fig. 1. 



f ' On the London Clay Formation,' Charlesworth's Magazine of Natural History, new series, 

 iv. p. 24 ; figures in text. J In Dixon's « Sussex,' p. 138, pi. i. fig. 5. 



