chief Generic Types of Palceozoic Corals. 455 



lamella of the central area are truly the septa, and in his not 

 having detected the constant presence of a columellarian line 

 in the centre. 



At a later period, Mr. Billings (Can. Joum. new ser. vol. iv. 

 p. 128, 1859) defined the genus as similar in structure to 

 Zajyhrentis, except in the possession of an exterior zone of 

 vesicular tissue and in having the tabulaj " elevated in the 

 centre so as to form a small conical protuberance in the bottom 

 of the cup." A single species, from the Devonian formation 

 of Western Ontario, was referred to the genus under the name 

 of C. oneiclaense. We have satisfied ourselves, however, from 

 the examination of a large number of specimens, that the struc- 

 ture in C. oneidaense, as well as in the related C. plariradiale^ 

 Nich., is essentially different from that oi CUsiophyUuni proper ; 

 and we propose to found for these two forms a new genus under 

 the name oi Acrophjllum* . 



The definition of the genus Clisiopliyllum given by Prof. 

 De Kouinck (Anim. Foss. Nouv. Recherches, prem. partie, 

 p. 39, 1872) is in most respects similar to that given by Milne- 

 Edwards and Haime. The septa are described as extending 

 to the centre of the calice ; and the columellar plate is stated to 

 be a prolongation of the principal septum. 



Much the same view of the structure of the genus is taken 

 by Dybowski (Mon. der Zoanth. scler. nig. p. 82, 1873), who 

 places Clisiophyllum in the immediate neighbourhood of Litho- 

 strotion, and defines it as having septa which closely embrace 

 a freely projecting columella, and elevate themselves to form 

 collectively an eminence in the centre of the calice. 



When we come, however, to investigate the aflfinities of 

 Clisiophyllum^ it is at once evident that it has little real rela- 

 tionship with Lithostrotion. Not only is the latter invariably 



* A brief diagnosis of this genus may advantageously be appended in 

 this connexion : — 



AcROPnYLLUM, Tliomson and Nicholson. 



Gen. char. Corallura simple, turbinate, or cylindro-conical. Epitheca 

 thin, with numerous encircling striie and amiulations of growth. Central 

 area occupied by strong tabulse, which are not vesicular, and are very 

 strongly elevated centrally, and at the same time more or less twisted 

 with a spiral bending, so as to give rise -to a central funnel-shaped and 

 obliquely contorted eminence. This eminence is formed solely by the 

 elevation of the successive tabuhe ; and no vertical plates take part in its 

 formation as is the case in Clisiophi/llum. The septa are well developed, 

 lamellar, usually prolonged over the upper surfaces of the tabuhe in the 

 form of striffi which extend nearly to the centre. Ivvternal area traversed 

 by the septa, which are united by comparativelv remote angular dissepi- 

 ments. No rolunif^lla. A well-marlved septal fossette. 



Tvpe sp. Arrojihi///i(i)i onridncuxc, liill. 



