146 MADREPORARIA. 



Only small stocks could tlevelop 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, Ijetween 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 memln-anous walls and septa, very wavy and twisted so as to form 

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

 forms frequently show also a great development of tabuloe (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 (PL X". 

 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 iu 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 PL X. fig. 5). This is also the case with specimens of G. Sussev 1, whicli, as 

 Litharcm Wcbsteri, was the type of the genus Litliarma (see PL X*. fig. 7). Absence of pali 

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

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

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

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

 sufiiciently 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 lieing so distinguished. A few words will suffice to .show that no generic 

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

 of pali. For not only have several Litharmm been described with developed pali (e.g. fcr. 

 Vicenza 3, 5, S, see also distinct traces of paLi in PL X. fig. 2), but a tendency to the 

 obscuration of the pali is quite observable in recent foi'ins whenever the calicles are gaping 

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

 PI. VIII. fig. 6). 



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

 D'Achiardi spoke of one of the former as if it had just come fresh from the sea, and Eeuss 

 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 with 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 grou]3s seem to range from Lower to 

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

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



