164 PROF. W. H". BENSON AND DR. S. SMITH ON [vol. lxxix r 



before or after this divides into the cardinal and counter-septa. 1 

 In some cases the columella remains united to both septa, 1 in 

 others, to either the counter or cardinal septum ; while, in yet 

 other instances, it becomes separated from both septa. 3 The 

 medial plate, as in Amygdalophyllam, represents part of the 

 original axial septum. 



The columella in Amy gdalophyllum is very much larger than is 

 normally found in .Rugose Corals ; but three other genera are- 

 known to us which have columellse of a similar t} r pe : namely, 

 Gyathaxonia, Carruther sella, and Cionodendron. 



Cyathaxonia Michelin, 3 a simple Zaphrentoid coral of which 

 several species have been described, gives its name to the highest 

 of the Avonian zones established by Arthur Vaughan in the 

 British Isles. It is widely spread in Britain, and is also found in 

 the Tournaisian of Belgium. The genus was discussed by Mr_ 

 R. G. Carruthers in 1910. 4 According to his figures, the columella 

 has the same radial and concentric structures as that of Amygdalo- 

 phylhtm, but the septa do not enter it. 



Carruther 'sella compacta is also a simple form, and was de- 

 scribed by Prof. E. J. Garwood. 5 It appears to be allied to the- 

 Clisiophyllid genera. The columella contains a medial plate and 

 embedded ends of septa ; it is described by Prof. Garwood as 



' solid and conspicuously spindle-shaped . . . composed of a narrow plate from 

 which radiate . . . 6 closely packed lamellae, usually in contact throughout this 

 area : the majority of these lamellae are directly continuous with the 

 attenuated ends of the major septa ; occasionally, additional lamellae appear 

 to be inserted, and occupy positions facing the minor septa, but these do not 

 as a rule reach the central plate.' 



These words equally well describe the columella of Amygdalo- 

 ■phyllum and Cionodendron. Carruther sella was obtained from 

 the Tournaisian rocks 7 of the North- West of England (Meathop 

 Fell, near Arnside, Morecambe Bay). Cionodendron columen,. 

 the species to be described later, is a composite form derived from 

 Lithosirotion. It is, broadly speaking, from the same region and 

 horizon as Amygdalophyllum, although not from exactly the same 

 locality, nor necessarily from precisely the same stratigrajmical 



1 In previous studies (Q. J. G. S. vol. lxxi, 1915-16, p. 231, and elsewhere) 

 one of us (S. S.) has spoken of the columella as derived from the counter- 

 septum ; this is not invariably so, and the emendation here made appears to 

 accord more closely with, the facts ascertained. 



2 Frequently, however, the union between the columella and the septa or 

 septum is only maintained by an exceedingly thin isthmus of tissue. 



3 Congres de Turin, 1840. 



4 Geol. Mag. pp. 53-56, & pi. iii, figs. 4-10. 



5 Q. J. G. S. vol. lxviii (1912) pp. 555-56 & pi. xlviii, figs. 1 a-\ d. 



6 The three words omitted after ' radiate ' are ' fifteen to twenty ' ; but the 

 figures show about this number of lamellae on both sides of the medial plate : 

 that is, double the number. 



7 From the summit of the Seminula-gregaria subzone (upper part of the 

 Athyris-glabristria Zone) of Prof. E. J. Garwood, a horizon equivalent to the 

 lower part of the Upper Syringothyris Zone (C 2 ) of Arthur Vaughan. 



