44 ME. J. A. DOUGLAS ON GEOLOGICAL SECTIONS [vol. lxxvi, 



not attached undue importance to this modification of structure, it 

 may be said that the dominant ' tone ' of the age was Lopho- 

 phylloid. 



In the absence of any known Lower Avonian corals from South 

 America, a direct descent from a true Zaphrentid ancestor along 

 any known gens-line cannot at present be definitely proved. It 

 I has not been thought advisable, however, to institute distinctive 

 generic names for these new forms until such a possibility is denied. 

 I have, therefore, restricted myself to the use of such terms as 

 ' Lophophylloid Zaphrentis, ' thereby implying a coral having the 

 typical structure of a Zaphrentis combined with an essentially 

 Lophophylloid columella, which, unlike that of a Cyathaxonia, is 

 a direct continuation of the counter-septum. The relationship of 

 any of these forms with Cyathaxonia is more superficial than real, 

 although an occasional individual section may reveal a disposition 

 of septa suggestive of a Cj^athaxonid tj r pe of structure. 



In one example (PI. I, figs. 9«-9e) the inner ends of the septa 

 are fused Avith a thick stereoplasmic lining, the continuity of 

 which is broken by the cardinal and alar fossuhe. 



In earlier stages of growth, however, increased thickening often 

 results in the formation of a confused central mass, the nature of 

 which is not apparent until further sections are cut from the same 

 specimen. The columella!' thickening of the counter-septum and 

 the club-shaped extremities of the other major septa are then seen 

 to have their origin in this stereoplasmic lining, and, where the 

 latter wraps round the ends of the septa without forming complete 

 contact, a series of hollow terminal tubes is produced. 



It thus becomes apparent that, although the final result attained 

 (an increase of strength in the corallum) is the same in many 

 cases, homogenesis of structure must by no means be taken for 

 granted. 



Lophophylloid Zaphrentis. (PI. I, figs. 8a-8/, 9a-9e.) 



Description. — Corallum simple, conical and cornute. Epitheca strongly 

 costate : alternate sulci corresponding to internal septa. Floor of calyx 

 radiated by a single series of 22 well-spaced major septa. Cardinal septum 

 short, situated on the concave side of the corallum. Fossular depression 

 ill-defined. 



Counter-septum long, extending to the centre of the corallum, and 

 thickened at its inner end to form a laterally-compressed plate-like columella. 



Horizontal sections. — In the earlier stages of g-rowth the septa are 

 distinctly Zaphrentid in character, the cardinal and alar breaks being well- 

 defined. The septa are considerably thickened, and show a curvature convex 

 to the cardinal fossula. The latter is at first wide, narrowing inwardly, but 

 in the adolescent stage, owing to the growth of new septa in the cardinal 

 quadrants, becomes somewhat constricted at its centre (fig. 8d). In the 

 mature stage, the septa, with the exception of the counter-septum, are thin 

 and Amplexoid in character, having become entirely separated at the centre of 

 the corallum. The cardinal fossula is inconspicuous, being indicated merely 

 by a shortened septum. 



Minor septa are absent or undeveloped. Tabular intersections are rare. 



Vertical section. — Tabulae are seen to be few in number and widely 

 spaced (fig. 8/). They are gently arched towards the calyx, and dip some- 



