146 MADKEPOKARIA. 



Only small stocks could develop on a substratum which supplied no solid foothold, and 

 only corals whose skeletons were adapted to enable the individual polyps to cope with 

 deposits of sand-grains could survive. It is for this latter purpose I would suggest that 

 the extraordinary proliferation of the intra- calicular skeletons of so many of the Paris Basin 

 specimens may be due. A close network would form a better support to the delicate walls in 

 the event of sand settling on the calicles than a series of straight radial septa, between which 

 the sand-grains might sink. 



The specialisations seem to have travelled along three lines : — (1) They may form pro- 

 liferations of the synapticular outgrowths, shown in the group illustrated on PI. X. figs. 1-8. 



(2) They may have smooth membranous walls and septa, very wavy and twisted so as to form 

 a flaky reticulum (see PI. X. fig. 9, PI. X a . figs. 1, 2, 5-8, and X". figs. 1 and 2). These 

 forms frequently show also a great development of tabulae (see PI. Xa. figs. 1 and 2); and 



(3) they may show a striking diminution in the size of the calicles, departing from the typical 

 septal formula of Goniopora, and taking on the appearance of a Poritcs. The skeleton is 

 then a very close and compact reticulum, and the interspaces necessarily very minute (PI. X a . 

 figs. 3 and 4). 



I would not assert that it is possible to divide the specimens into true genetic groups 

 along these lines, but only that there is a very marked tendency of the Paris Basin forms to 

 be specialised in one or other of these directions. 



The first of these groups has some historical interest. It contains several forms with 

 shallow gaping calicles and large spongy columellar tangles, the latter showing no traces of 

 pali (see PI. X. fig. 5). This is also the case with specimens of G. Sussex 1, which, as 

 Litharcea Websteri, was the type of the genus Litharcea (see PI. X 6 . fig. 7). Absence of pali 

 was naturally given as one of the characters distinguishing this genus from Goniopora and 

 from Rhodarcea ; indeed the three genera, it was thought, formed a series : — Litharcea without 

 pali, Goniopora with pali in the " young " calicles but disappearing in the " adult," and Rhodaraa 

 with pali always forming a conspicuous rosette. As between the last of these two we have 

 sufficiently discussed this supposed generic distinction in the Introduction to this Volume, 

 and have pointed out at the same time that Milne-Edwards' " young " and " adult " calicles do 

 not admit of being so distinguished. A few words will suffice to show that no generic 

 distinction can be established between Litharcea and Goniopora upon the presence or absence 

 of pali. For not only have several Litharcece been described with developed pali (e.g. G. 

 Vicenza 3, 5, 8, see also distinct traces of pali in PI. X. fig. 2), but a tendency to the 

 obscuration of the pali is quite observable in recent forms whenever the calicles are gaping 

 and shallow, with large reticular columellar tangles (see, for instance, PI. IV. fig. 9 and 

 PL VIII. fig. 6). 



As compared with the fossil Gonioporce from Italy and Austro-Hungary, even though 

 DAchiardi spoke of one of the former as if it had just come fresh from the sea, and Beuss 

 figures much fine detail, the French representatives of the genus are more uniformly well 

 preserved. The finest details of structure are nearly always recognisable. Add to this the 

 facts (1) that the Paris Basin forms appear to have been an isolated group, and (2) that they 

 show specialisations of structure not elsewhere met witli in any other part of the world, and 

 we have ideal conditions for the careful local study of the genus in relation to the different 

 horizons at which specimens occur. The Paris Basin groups seem to range from Lower to 

 Upper Eocene ; I would suggest that a study of all the available Goniopora material now 

 stored in French museums, added to by fresh finds when the localities are revisited, would 



