B. G. Carruthers — Remarkable Carboniferous Coral. 437 



which eventually become the alar and the counter-lateral primaries 

 (A and CL in Diagram, Fig. 2). One of these pairs may precede 

 the other, or they may appear simultaneously, but in any case they 

 move outwards until approximate symmetry is attained ; the primary 

 stages, resulting in the formation of six septa, are then complete 

 (Diagram, Fig. 2). All subsequent major septa (" metasepta" is 

 the convenient term for them proposed by Duerden) are inserted 

 according to an invariable rule: in the two "main" sectors H-A 

 (Diagram, Fig. 3) the newest are those next to the main septum H, 

 in the alar sectors A-CL they are next to the alar primaries A, in 

 the counter-lateral sectors CL-Gr none ever appear. From this 

 results the well-known pinnate disposition of the septa seen after 

 removing the epitheca from the conical portion of a Rugose coral (the 

 part, that is, wherein there is a continuous addition of new septa). 



In addition to the major septa, many species have a cycle of minor 

 septa. These are relatively short and are most often a feature of adult 

 growth-stages. They appear simultaneously, one between each major 

 septum, those in the two counter-lateral sectors CL-G often being 

 longer than the others : sometimes there are two minor septa only, 

 in which case they are restricted to the two counter-lateral sectors, 

 one on each side of the counter-primary G. Where seen, this factor 

 is of much value in the orientation of transverse sections. 



The foregoing scheme of septal development is applicable to all 

 manner of Rugose corals, but in the genus Cryptophyllum, now under 

 review, it is very curiously modified. 



Development of Crypt ophyllvm. 



Cryptophyllum hibernicum is a small solitary coral, tortuous in habit, 

 with a smooth concentrically ribbed epitheca (PI. XI, Fig. 5). It is 

 easy to distinguish from other Carboniferous corals, immature 

 specimens displaying five septa only, while even in adults these five 

 septa remain predominant (PL XI, Figs. \j, 2c, 3h). The special 

 developmental features of the genus are easily followed in a set of 

 serial transverse sections. 



Very commonly there are no traces of septa whatever in the earliest 

 growth stages, the corallum being purely tabular (PL XI, Fig. la). 

 Later on septa appear, initially as minute protuberances from the wall, 

 each with a dark centre (PL XI, Fig. lb) : generally they increase in 

 length until five septa are formed, meeting in the centre of the 

 corallum (PL XI, Figs. l/and3/). These five septa are not inserted 

 in any regular order, and they are frequently affected by growth- 

 constrictions (or "rejuvenescence") of the corallum, leading to a 

 retraction or even obliteration of one or more of their number 

 (cf. Figs. 3c and 3d, PL XI) : not infrequently, the rejuvenescence is 

 so extreme that a resumption of the tabular, non-septal condition is 

 brought about. Eventually, however, the five-septal stage is established 

 on a more or less stable footing, and may persist for some time. 

 It has been arrived at, as we have seen, in an altogether hesitating, 

 wayward manner, and is so unlike anything seen in the early stages 

 of normal Rugose corals that were no further evidence available, one 

 might justifiably suspect that an entirely new order was under 



