LoiDhopliylluin and Cyathaxonia. 53 



Acrophyllum,^ should be abandoned, on the score of priority, in t'a\ our of 

 Lophophyllum, of which an amended diagnosis may be given as follows : 



Corallum simple and turbinate. Major septa meeting in the centre 

 of the coral in the early growth-stages. One of the septa, usually 

 the counter septum, is strongly thickened at the inner end, giving 

 rise to a prominent columella, which may be discontinuous. In the 

 more mature growth-stages the columella persists, but the septa 

 usually retreat from the centre and become amplexoid, while dis- 

 sepiments appear between the tabulae and the wall. The tabulae are 

 arched upwards in the centre to a varjnng degree, but, unlike such 

 genera as Bihunophyllum, there is no central zone where the tabulae 

 are more numerous or vesicular, nor is there a system of vertical 

 lamellae distinct from the septa. 



Those corals referred by Nicholson & Thomson and other authors 

 to Lophophyllum (e.g. L. proliferum and L. eruca) do not develop 

 dissepiments at any stage of growth, and are essentially Znphrentes 

 having one of the septa thickened at the inner end. It may be con- 

 venient at some future time to group them as a sub-genus of Zaphrentis, 

 but for the present such a course is not considered advisable. 



Noten on the Lophophylluid columella. — The columella of a Lopho- 

 phyllum is not, as in Cyathaxonia, a structure independent of the 

 septa ; on the contrary, it is simply a direct continuation of one or 

 more of the major septa (usually the counter septum, sometimes of 

 the cardinal or other major septa in addition). This fact is brought 

 out on examining a thin vertical section, cut as nearly as possible 

 down the centre line of the counter septum. Such a section is shown 

 on PL III, Fig. 3, the subject being a ' LConinckophyllum ' from the 

 Scottish Lower Limestone Group (approximately of Dg age). In this 

 section the fine radiating striae represent the crystalline fibi'es of 

 the skeleton ; these spring from dark points, which are arranged in 

 ill-defined linear series, one for each layer of growth. When these 

 lines are followed inwards from the outer end of the septum (right- 

 hand side of figure) they are seen to curve downwards and then 

 gradually rise towards the centre of the coral, where they have 

 a dome-like arrangement (the 'columella'). It is accordingly clear 

 that there was coptinuous deposition of material along the upper 

 edges of both septum and ' columella', and that the latter is, essentially, 

 a mere continuation of the septum. The case is diff'erent in Cyathaxonia, 

 as vrill presently be shown. 



Genus CYATHAXONIA, Mich. (PI. Ill, Figs. 4-10.) 



The genotype of Cyathaxonia may be taken as C. cornu"^ ; as in the 

 preceding case, the type-specimen is lost, but the original figures 



' Thomson was mistaken in his conception of this genus, which was distinctly 

 stated by Nicholson to have no columella. Good figures of the genotype, 

 A. oneidense (BiUings), are given by Lambe in Contrib. to Canadian Pal., 

 vol. iv, pt. i, pi. xvi, figs. 1, 2, 1899. 



- No genotype was given by Michelin ; Milne-Edwards and Haime selected 



fC. cornu, and their example is here followed, for reasons which will be 

 explained in detail elsewhere. This course does no injustice to Michelin : 

 whereas a rigid interpretation of the law would necessitate a radical change in the 

 long-established conception of Cyathaxonia, and this for purely academic reasons. 



