jR. O. Carrtithers — A Revision of some Carboniferous Corals. 161 



epitheca. Longitudinal ribbing is practically absent, although faint 

 indications may be occasionally observed. 



The calyx is deep in young specimens, becoming on the whole 

 shallower with increasing age. The nature and arrangement of the 

 major septa are greatly dependent upon the habit of growth, and age, 

 of the coralluin, and since they vary within somewliat broad limits, 

 many names founded on the aspect of the calyx, have been applied to 

 the one species. When growth is perfectly uniform, gradual 

 and successive changes in the development of the septa take place as 

 the coral grows older and more cylindrical. Before considering 

 modifying factors, the history of the calyx, in such regular specimens, 

 may first be detailed. 



Commencing with young examples [^ Zaphrentis vermicular is, ^ 

 de Kon.), the uniformly thin major septa usually reach the centre 

 of the calyx (often anastomosing in an irregular manner), though 

 some may fall short and join their neighbours; the long counter 

 septum is frequently so connected, and often remains a prominent 

 object until the cylindrical stage is reached, or even throughout 

 growth. In these young examples, the (cardinal) fossula is very 

 marked and deep, extending with parallel walls to the centre of the 

 calyx. Minor septa are not yet apparent. From the species founded 

 on such young examples, this may be termed the vertnicularis phase. 

 . As growth proceeds, the major septa may continue to reach 

 the centre of the calyx for some time, their arrangement becoming- 

 very regular {'■ LopJiophyllum JDumonti,'' M.-Ed. & H., and Zaplirentis 

 cornucopia, de Koninck, Nouvelles Recherches, pi. x, fig. ba) ; the 

 counter septum continues prominent and the rudimentary minor 

 septa make their first appearance. This period may be called the 

 dumonti -phase. Beyond this the septa begin to fall short and leave 

 a smooth bare tabular area (about 2 mm. in diameter) in the centre 

 of the calyx floor, which forms the inner end of the cardinal fossula 

 (see PI. YI, Fig. 2). The expansion of the coral now becomes less 

 rapid, the calyx shallows, while the septa retreat further from the 

 centre and the cardinal fossula becomes shorter and rather broader 

 (' Zaphrefitis nystiana,' de Kon.); this may be called the nystiana 

 phase. 



A thin ring of dissepiments next appears around the internal 

 margin of the calyx, thinning away near the rim,' while the central 

 tabular area now amounts to one-third the diameter of the calyx 

 {' Zaphrentis edivardsiana,' de Kon., see PL YI, Fig. 4). "With further 

 growth the coral becomes cylindrical, and only a slight change is 

 manifested in the calyx. The septa, however, may become still 

 shorter, so that the bare tabular area increases up to one-half the 

 diameter of the coral. The cardinal fossula may also shorten and 

 form a marginal, but still distinct, depression of the calyx floor (see 

 PL YI, Fig. 1^). The dissepiments do not increase in number or 



1 This feature, though not dii-ectly referred to by de Eoninck, is seeu in the type- 

 specimen of his Zaphtrntis edwardiiana. As the epitheca of that species is of 

 medium thickness, the recognition of the dissepimental margin may be included in the 

 words " epitheque tres epaisse," given in his diagnosis. 



DECADE V. — VOL. Y. NO. IV. 11 



