580 MR. J. A. DOUGLAS ON THE [Nov. 1909, 



Diphyphyllum. 



Diphyphyllum aff. subibicinum (M'Coy). (PI. XXVII, fig. 13.) 



A form somewhat similar to that described by Dr. Vaughan 1 

 occurs at the base of D„ in County Clare, associated with Campo- 

 phyllum aff. marginatum, Thomson. 



Lithostrotion. 



Nematophyllum(Lithostrotion) minus, M'Coy. (PI. XXVII, figs. 1, 

 2a, &2b.) ^.-r/vV-AL 



M'Coy, Ann. & Mag. Nat. Hist. ser. 2, vol. iii (1849) p. 17 ; and ' Brit. 

 PaL-eozoic Fossils ' 1855, p. 99 & pi. iii B, fig. 3. 



A form which occurs in great abundance, and constitutes a definite 

 horizon near the summit of S 2 in County Clare, bears a close 

 resemblance to M'Coy's species. The type, figured in his ' Palaeo- 

 zoic Fossils,' which is now in the Sedgwick Museum at Cambridge, 

 is but a poorly preserved specimen, and a description of this species 

 from further material seems desirable. 



The corallites are slightly larger than in the Clare form, but a small 

 fragment, polished to show a vertical section, appears to have an 

 identical structure. 



The following is an emended description of this species : — 

 Corallites prismatic, with rarely more than sis sides : average dia- 

 meter = about 3 lines; epitheca, when visible, exhibiting longi- 

 tudinal striations. M'Coy's distinction between separable and 

 non-separable corallites does not appear justifiable, as in many 

 cases this is merely a matter of fossilization ; specimens from the 

 same bed differ widely in this respect, though identical in a thin 

 section. 



Vertical section. — The centre of the corallite is occupied by 

 a thin rod-like columella, measuring about half a line in width ; 

 inner area composed of slightly curved vesicular plates, with their 

 convex sides directed outwards and upwards ; and it takes as a 

 rule about three plates to reach from the axis to the external 

 boundary of the area. 



The outer area is of approximately the same width as the inner : 

 it consists of four or five rows of vesicular plates, of smaller size 

 and more regular arrangement than those of the inner area, and 

 having their convex sides directed upwards and inwards. 



Horizontal section. — Boundary between individual corallites 

 well marked. Columella usually ill-defined, compressed laterally. 



The septa average 42 in number, and the major and minor series 

 are of equal thickness. The former reach the columella, but the 

 latter only project a short distance beyond the inner wall. The 

 medial area comprises about three rows of obscure vesicles, bounded 

 by a more or less distinct inner wall. The external area has five or 

 more rows of vesicles, with, as a rule, a regular concentric arrange- 

 ment. 



1 Quart. Journ. Geol. Soc. vol. lxiv (1908) p. 461 & pi. xlix, fig. 7. 



