Vol. 69.] THE GEXUS AVLOPIIYLLCM. 5 ( .» 



the very graceful curvature so characteristic of Zaplirentis is 

 comparatively rare. Od the other hand, I have not seen a single 

 example of the turbinate form, so common in Dibunophyllum, 

 although obtusely turbinate members of that genus are found 

 associated with Aulophyllum at Peterhill. The calyx is moderately 

 deep, and possesses a stout "wall. From its depressed base there 

 generally rises a prominent protuberance (the central column) 

 (fig. 1 A); but in some cases this feature is so inconspicuous (fig. IB), 

 that a longitudinal section is required to demonstrate the presence 

 of this feature. The middle of the central column is usually 

 occupied by a small pit. The fossula is not easily seen, but is 

 nearly always situated on the convex side of the corallum. The 

 appearance of the calyx in many specimens is greatly modified by 

 corrosion prior to entombment, as well as by subsequent weathering 

 in the exposed rock. Slight constrictions are frequent, and give 

 rise to ridges encircling the corallum, which converge and even 

 intersect on the concave side in its trochoid stage, but are parallel 

 in the cylindrical. The more marked constrictions, due to rejuven- 

 escence, are of less common occurrence. 



(2). Internal characters. — Since structural details will be 

 fully treated in subsequent sections of this paper, it is here 

 necessary to outline only the general plan of coral anatomy. The 

 corallum, if its very young stages be disregarded, may be considered 

 as built up of three concentric cones : — 



(i) An innermost cone (the central column). This is formed of 

 irregular vesicles, the innermost members of which are 

 small and concave towards the calyx, while encircling 

 them are plates bent towards the proximal end of the 

 corallum into an almost vertical position (as, for example, 

 fig. 4b in PI. VI). These outer vesicles form the ' wall' 

 of the central column. The inner vesicles will be re- 

 ferred to as ' central vesicles,' and the outer vesicles, for 

 the sake of distinction, as ' pericentral vesicles.' These 

 vesicles are cut by vertical plates (the septal lamellae) 

 which radiate inwards from the boundary of the column. 

 The boundary of the column is almost regular ; but 

 there are slight indications of alternating restricted and 

 bulging portions. 



(ii) A middle cone, in which large irregular vesicles (the tabular 

 vesicles) 1 lie inclined from the central column, and are 

 convex towards the exterior of the corallum. A single 

 flattened vesicle may extend across the zone, but usually 

 two, three, or even more are required to bridge the 

 space. 



' Inner dissepiments ' of most author; 



