Professor E. J. Garwood — Rock-building Organisms. 265 



Fig. 20. Cristellaria cephalotes, Eeuss. 

 ,, 21. Ilhabdogoni2im insigne, Fieuss. 21a, lateral aspect ; 216, oral aspect. 

 ,, 22. Nodosaria {Dcntalina) legumen, Eeuss. 

 ,, 23. Marginulina debilis, Berthelin. 

 ,, 24. Nodosaria (Dentalina) communis, d'Orb. 

 ,, 25. Cristellaria rotulata (Lamarck). Magnified 33 J diameters. 

 ,, 26. C. gracillissima, Reuss. 

 ,, 27. C. gauUina, Berthelin. 



(To be concluded in the next Number.) 



III. — Some new Kock-building Organisms from the Lower 



Carboniferous Beds of Westmorland. 



By Professor E. J. Garwood, M.A., F.R.S., F.G.S. 



(PLATES XX AND XXI.) 



IN my account of the Lower Carboniferous rocks of the North- West 

 of England, published in 1912, I figured an organism, probably 

 the thallus of a calcareous alga, which plays an important part 

 as a rock-builder at the base of the Semmula gregaria sub-zone in 

 Westmorland and Lancashire.^ More recently, at the meeting of 

 the Briti8h Association in Birmingham,- I pointed out the need of 

 some distinctive name for this important form, and suggested for 

 it the generic name of ' Ortonella ', from the village of Orton, near 

 Tebay, in the neighbourhood of which this fossil is sjtecially abundant. 

 Two other structures were mentioned at the same time which 

 occur constantly in microscopic sections of the Lower Carboniferous 

 rocks of the North-West of England and elsewhere. The first of 

 these was alluded to under the general descriptive term ' festoon 

 structure', and the other was referred to Giirich's somewhat obscure 

 genus Spongioxfroma. In view of the zonal value of these organisms 

 in the North-Western Province and the probahility that they will be 

 found to be widely distributed in the Lower Carboniferous rocks 

 elsewhere, I propose here to give a somewhat fuller description of 

 these forms than could be attempted in the limits of a presidential 

 address. 



Ortonella, gen. nov. (PI. XX, Eigs. 1-4.) 

 Mode of Occurretice. — The remains of tliis organism occur in the 

 form of sub-spheroidal nodules varying in size from that of a marble 

 to that of a tangerine orange, tlie largest example met with having 

 a diameter of 5 cm. (Fig. 1). The fractured surfaces of the nodules 

 show a porcellanous texture and a uniform rich brown tint, while 

 a distinct concentric arrangement is usually noticeable. In trans- 

 parent slices a fibrous structure radiating from the centre can also be 

 observed with a strong hand lens. The smaller examples resemble, 

 in general appearance, the nodules of Solenopora which occur in the 

 underlying sub-zone in Westmorland and likewise the nodules of 

 Mitcluldeania which are found so abundantly in the Lower Carboni- 

 ferous deposits of Mitcheldean and North Cumberland. 



Under the Microncope. — The thallus is seen to consist of a series of 

 fine ramifying tubes which radiate from the centre of the nodule in 



' Q.J.G.S., vol. Ixviii, p. 449, pi. xlvii, fig. 2, November, 1912. 

 - Rep. Brit. Assoc. 1913, Section C; also Geol. Mag., Dec. V, Vol. X, 

 pp. 440, 490, 545, 1913. 



