134 



PEOF. P. M. DUNCAN ON THE STRUCTUEE AND 



of Thamnastrcm Waltoni, Ed. and H., and had it figured (Pal. Soc, 

 pt. iii. pi. xi. figs. 6-9). Mr. Tomes says : — " The figures given 

 by Dr. Duncan as of this species, but unaccompanied by letterpress, 

 must, in my opinion, be referred to some other species which has 

 the septa more strongly geniculated." In other words the geniculate 

 condition of the form is greater than in the true type of Thmnnastrcea 

 Waltoni. Now on looking at the figures, it will be noticed that there 

 is very slight geniculation — it could hardly be slighter. It was 

 this want instead of excess that made me doubt for a while about 

 the identity of the form and the species Waltoni, 



Mr. Tomes communicated to the Society his essay " On some 

 imperfectly known Madreporaria from the Coral Eag and Portland 

 Oolite of the Counties of Wilts, Oxford, Cambridge, and York " in 

 1883 (Quart. Journ. Geol. Soc. vol. xxxix. p. 555). 



It is very satisfactory to be able to agree with the author in most 

 of the descriptions and opinions given and expressed in this commu- 

 nication ; nevertheless there are some points on which there is 

 considerable difference between us. 



It is to be noticed with some satisfaction that the genus TJiamn- 

 astr(Ea is partly taken out of the Perforata and restored to the 

 Pungidse. But it is to be gleaned that the author still inclines 

 to place the species with perforate septa in the section Perforata. 

 It is proposed to separate the perforate and imperforate Thamnas- 

 trseans into dijfferent genera ; but the answer to this proposition may 

 be gleaned from what has already been written elsewhere. In some 

 Thamnastrseans the septa are perforate, thanks to fossilization, in all 

 their laminae ; in others of the same species only parts of the 

 corallum have their septa perforate, the rest being imperforate. 

 The same species will be found under different circumstances to 

 present perforate and imperforate septa. Unless we are to have 

 the novelty of two genera in one individual the proposition of 

 dividing the Thamnastraeans must drop. 



The figures given by Mr. Tomes on plate xxii. of T. concinna, 

 Goldf., sp., are very remarkable, and they explain why the author 

 stated, " These often exhibit forms so remarkable as to suggest spe- 

 cific or almost generic distinction, and thev deserve especial notice " 

 (p. 559). 



They really present so many resemblances to a Stylina and so few 

 to Thamnastrcea concinna that it is to be hoped careful sections will 

 be placed where they can be studied. 



IsASTEJSA OBLONGA, Ed. and H. 



The distinguished authors of the ' British Eossil Corals ' are said 

 to have overlooked the real characters of this species. They 

 were misled by the state of fossilization. The foUowiog is the 

 statement of Mr. Tomes (p. 563) : — " By selecting specimens in 

 which the silicified corallites are less deep in colour the details of 

 structure are more readily seen, and the wall is observed to be thin 

 and to be lined within with a considerable quantity of dissepi- 



