L. M. Parsons — -Carboniferous Limestone of the Wrekin. 7 7 



shape of the theca ; for co-channels are clearly represented in the 

 drawing of IT. splmroidalis Miller & Gurley (1895); the drawings 

 of R. canneus Miller (1889), and H. hammelli Miller (1889), seem 

 intended to show them; irregular peripores are represented in 

 H. adipatus Miller (1891), H. ampins Miller (1892), and JS. gijrinus 

 Miller & Gm-ley (1894), and seem to have been observed in 

 H. dyeri Miller (1879), and possibly IT. ventricosus Miller (1879). 

 Examination of twenty-seven specimens from the Osgood Limestone 

 of Big Creek, now in the British Museum, show that, whatever the 

 differences of form or surface ornament, all possess or possessed 

 co-channels. Among these specimens are some determined (rightly 

 or wrongly) by Miller himself as H. scitulus (E 16167-8-9) and 

 H. globosus (E 16170-1). If Miller did not observe the co-channels 

 in these and other species, that may be due to the facts that on well- 

 preserved surfaces they are not clearly exposed (E 7673, E 16167), 

 and that on much-weathered surfaces they have often been worn 

 away (E 16171). The reason for this will appear later; for the 

 present I confine myself to the preceding justification of the belief 

 that all Miller's species did have co-channels, whether he said so or 

 not. This, then, leads to the further conclusion that the species from 

 the Racine Limestone also had co-channels; at any rate their general 

 resemblance is such that the burden of proof lies on those who 

 would deny this conclusion. Finally it follows that all . the 

 American species belong to a single genus, for which Hall's name 

 Megacystis (-ites) should be adopted. 



It may here be suggested that Allocystites Miller, 1889, with 

 genotype A. hammelli, from the Niagara group of Jefferson co., Ind., 

 is a Megacystis. Jaekel (1899, p. 398) placed it in the Sphaaronidse, 

 believing that the pores were diplopores. I would go further, and 

 point out that the drawing of these pores (Miller's fig. 242) indicates 

 the presence of co-channels. The unique holotype is drawn and 

 described as having a raised margin to the periproct, and the 

 peristome "covered by minute plates forming a pentagonal star". 

 Possibly! but one cannot help doubting whether Miller correctly 

 interpreted these peculiar appearances. There is already a 

 M. hammelli (Miller, 1889), probably a synonym of M. rotunda 

 (Miller, 1879). 



VI. — The Carboniferous Limestone of the Wrekin District. 



By L. M. Parsons, M.Sc, D.I.C, F.G.S. 



TPHE Carboniferous Limestone cropping out near Wellington and 

 X near Newport in the Wrekin district has hitherto received 

 little attention. One or two references to the Lower Carboniferous 

 rocks of the area are made in Geology in the Field, in which the 

 limestone is referred to the Dibunophyllum zone, 1 and the intrusive 

 material underlying the limestone is described as an olivine-dolerite, 

 probably of Tertiary age. 2 Apart from these references there does 



1 Geology in the Field, p. 762. 



2 Idem, p. 766. 



