Yol. 62.] IN THE CARBONIFEROUS ROCKS AT RUSH. 313 



In the South- Western Province this form is very abundant, and 

 characteristic of C and S r x 



A. planosulcata, Phil., has a circular and uniformly-convex form, 

 with a small pointed beak and uniplanar valve-intersection. The 

 typical form is abundant only in the highest beds of the Avonian. 



Camarophoria aff. isorhyncha (M'Coy). 



This fossil occurs, both in the Curkeen Limestone and in the 

 Cyathaxonia-Reds of the E,ush sequence. It differs from the form 

 recorded by Mr. Sibly from S x of the Weston area, 2 in having more 

 numerous ribs (which have a less outward sweep), and in the more 

 restricted lateral lunules. It differs from M'Coy's type 3 in being 

 much more compressed in thickness. 



Camarotgechia (?) an 2 , elexistria (Phil.). 



A single specimen from the Curkeen Limestone has its fold 

 scarcely differentiated, and the fold-ribs not appreciably larger than 

 those on the flanks. 



CORALS. 



SYRINGOPORA Cf. RETICULATA, Goldf. (PI. XXIX, fig. 1.) 



Tbe tubes are in parallel grouping, and, in a vertical section, at 

 about the diameter of a tube apart. The connecting-tubes are 

 short, and occur at points of approximation. 



In a chance horizontal section, the number of actually-connected 

 rings is relatively small, but the more closely-approximated pairs 

 indicate the presence of a connector within a short distance of the 

 plane of section. 



In the Hush sequence this Syringopora is common in, and 

 characteristic of, the Megastoma-Heds. 



In the South- Western Province a very similar form occurs 

 somewhat commonly in the Syringotliyris and Lower Seminula- 

 Zones, with which the Megastoma-Beds are here correlated. I 

 know, however, a practically-identical Syringopora from the Main 

 Limestone of Durham, a level which, judged by the associated fauna, 

 is unquestionably of Dibunophyllum-Sige. 4 



In my account of the Bristol sequence 5 I have pointed out that 

 the ' species ' of Syringopora are of the nature of circuli ; con- 

 sequently a correlation of two levels in distant localities, based 

 upon the similarity of the dominant Syringoporids, is partly 

 valueless. On the other hand, in the examination of a single area, 

 particular forms of Syringopora may be of great value. 



Stated broadly, dimensional variation is a function of 

 environment, whereas the degree of structural com- 

 plexity is dependent on the earlier history of the 

 gens, and is, consequently, a function of the time. 



1 T. F. Sibly, Quart. Journ. Geol. Soc. vol. lxi (1905) pp. 556, 557. 



2 Ibid. p. 557. 



3 ' Synopsis Carb. Limest. Foss. of Ireland ' 1844, pi. xviii, fig. 8. 



4 Specimens from Durham have been kindly submitted to me for examination 

 by Mr. J. T. Stobbs, F.G.S. 



5 Quart. Journ. Geol. Soc. vol. lxi (1905) p. 267. 



