﻿458 DE. A. YArGHAN OX THE FAUNAL SUCCESSION [Aug. I908, 



also the quadrantal arrangement of the septa into four stalked 

 groujDS — a striking feature of certain sections. 



rig. 6 6 is less distinctly fossulate and approaches Z. OmaJiusi 

 var. densa, Carruthers, ojy. cit. p. 29, pi. iv, figs. 7 & 8. 



Z. Omaliusi, var. ambigua and var. densa are the commonest 

 corals in the Rush Slates and in the Lane Limestone ; they also 

 occur rarely in the lower part of P. Their occurrence in other 

 areas has been described in § VI (pp. 440, 441). 



A Densiphylloid form of the Zaphrentis- Omaliusi group occurs in 

 the Lane Limestone, and ranges into the Lower P-beds. 



The adult is strongly Densiphylloid, and bears considerable 

 resemblance to the new species of Densiphylloid Zaphrentis 

 described below. In the adult the septa are straight and very 

 closely approximated, and the fossula is very inconspicuous. 



Young stages exhibit the typical plan of Z. Omaliusi, although 

 the greater number of septa is very noticeable. 



Mr. Carruthers identified a specimen of this form as : — 



' Cf. Z. Omaliusi, var. densa (occurs in the Millstone G-rit of Garnkirk).' 



Zaphrentis Omaliusi, var. ambigua, mut <t. (PI. XLIX, 



%. 8.) 



(!) Amplexus {Cyathopsis) cormc-bovis, Thorns. & Nich. op. cit. vol. xvii 



(1876) p. 65 & pk vii, fig. 6 1 ; non Michelin sp. 

 Compare Z. Omaliusi, var. ambigua, Carruthers, op. cit. p. 28 & pi. iv, fig. 6. 



This coral appears to be an example of phylogenetic old-age, 

 evident in : — 



(1) Its narrow, twisted form ; (2) The root-like excrescences and coarse 

 annulation of the epitheca ; (3) The thin, irregular, and crumpled 

 septa ; and (4) The strongly pronounced intermediates. 



Horizontal sections show great irregularity and variation of 

 septal plan. The one here figured illustrates the similarity of 

 phylogenetic old-age with ontogenetic old-age (as exhibited in 

 Mr. Carruthers's figure (loc. supra cit.) of an old individual of 

 the typical group). 



Most sections exhibit both counter and cardinal fossulae, the 

 former being the more conspicuous. 



The septa are spidery and, as a rule, continuously concave to the 

 cardinal fossula ; the counter-septa are closely packed and remark- 

 ably crinkled. Usually, the inner ends of the septa are fused 

 together at the centre, and in the calyx they produce a sharp 

 crest. 



This mutation has only been found in Ds^,, where it is not 

 uncommon ; the specimen figured by Thomson & Mcholson was 

 found in the Lower Limestones of Scotland. 



^ The figure of ' Amplexus cornu-bovis ' suggests a section of this species in 

 which the continuity of the septa has been destroyed ; I have obtained a 

 similar section from the figured specimen. 



