138 PKOF. p. M. DUl^CAN^ ON THE STEIICTUKE AND 



" But from the examination of a number of specimens from 

 Combe Down, I am convinced that the supposed columella does not 

 exist in any of them." 



Now there is nothing written about an essential columella in the 

 diagnosis of the genus Plerastrcea by its founders. Such a columella 

 arises from the base of the coral within and grows irrespectively of 

 any other structures, and the styloid columellse of Stylmce are 

 excellent instances. The columella in the form which first of all 

 came under the designation of Plerastrcea, P. Savignyi, Ed. & H., 

 has the " columelle papilleuse representee par des pointes du bord 

 interne des cloissons " (Hist. Nat. des Corall, p. 553, v. 2). Hence 

 in the diagnosis it is stated that the columella is '" papilleuse." 



As it was evident to Milne-Edwards and Jules Haime that 

 Plerastrcea Pratti, formerly called by them Clausastrcea Pratti, had a 

 fasciculate columella of the Plerastrsean type, and as it is to be seen 

 in their type specimen, any comparison of the form with one without 

 a columella is necessarily misleading. Mr. Tomes states that the 

 type was a worn specimen ; but had he seen it (unfortunately he has 

 not) he would have been able to bear out the correctness of the 

 description in the monograph of the British Fossil Corals. It is, 

 then, necessary to restore Isastrcea Conyhearii, Ed. & H., and Pler- 

 astrcea Pratti, Ed. & H., to their former positions, and the union 

 in a new genus Platastrcea is not requisite. 



Genus Bathtcqenia, Tomes. 



In the essay " On some imperfectly known Madreporaria from 

 the Great Oolite," p. 176, Mr. Tomes writes as follows : — " Great 

 doubt is expressed by Prof. Duncan, in his ' Eevision of the 

 Eamilies and Genera of Corals,' as to the distinctness of BatJiy- 

 coenia from Stylosmilia, which genus, in habit of growth, it some- 

 what resembles." He then proceeds to state that he had made 

 careful comparison of weU-preserved specimens of Tertiary Stylo- 

 smilice with BatJiycoenia, and that the absence of a true columella 

 was clearly made out. Now on turning to the "Eevision of 

 the Genera," p. 122, it will be noticed that no doubts whatever 

 were expressed about the distinctness of Bathycoenia and Stylosmilia, 

 The name of the last genus is not even mentioned, and what was 

 written in respect of the resemblances of Bathycoenia with another 

 genus, was copied from Mr. Tomes's own statements in his paper on 

 the " Great Oolite Madreporaria," 1883, p. 176. He there com- 

 pared the genus with two Tertiary species of the same genus, 

 Stylocoenia, which I mentioned in the " Eevision," 



At that time (Tomes, op. cit. p. 176) the genus Bathycoenia 

 had a " rugged columella ; " at the present time Mr. Tomes asserts 

 that it has none, in spite of the figures 8, 9, 10, pi. vii. of his work, 

 where the structure is well seen. 



The genus Stylosmilia is not known in the Tertiary strata. 



