468 TRANSACTIONS OF SECTION C. 
Ortonella. 
This form, as already mentioned, occurs in great abundance in the algal 
band in the ‘ Athyris glabristria zone’ of the North-West Province. It is 
found in spherical nodules up to the size of a small orange. In miscroscopic 
sections it resembles Mitcheldeania in so far as it consists of a series of tubes 
growing out radially from a centre. It differs, however, from this genus in 
many important respects. All the tubes are approximately of the same size, 
and there is no evidence of alternating coarse and fine tufts arranged con- 
centrically, as in the case of Mitcheldeania. Further, the tubes are not undu- 
lating as in that genus, and therefore in thin slices lie for a long distance in 
the plane of the section. They are much more widely spaced and show 
marked dichotomous branching, the bifurcations making a nearly constant angle 
of about 40°, and there is a strong tendency for the branching to take place 
in several tubes at about the same distance from the centre of growth, pro- 
ducing a general concentric effect in the nodule. 
The diameter of the tubes is decidedly less than those in Mitcheldeania, 
being usually little more than half the size of the larger tubes of M. gregaria. 
The nodules of this genus occur in great profusion, contributing largely to the 
formation of the shaley dolomite at the base of the ‘P. globosus band’ through- 
out the Shap, Ravenstondale, and Arnside districts in Westmorland and 
Lancashire. 
In addition to these genera there occur also two other encrusting calcareous 
growths which require mention. The first of these appears in thin sections in 
the form of a ‘festoon-like ’ growth, surrounding fragments of Calcareous Alge, 
especially Mitcheldeania and Ortonella. I have met with it abundantly in the 
‘Algal band’ in the North-West of England, but it also occurs not infrequently 
associated with Mitcheldeania in the Whitehead Limestone in the Forest of 
Dean, while a similar structure occurs associated with Mitcheldeania gregaria 
in north Cumberland. 
Although the exact nature of this growth is still undecided, I mention it 
here on account of its invariable association with undoubted Calcareous Alge. 
The other deposit is the form already alluded to under the term Sphero- 
codium, which I have found forming considerable masses of rock in many 
districts where the Lower Carboniferous beds are exposed; not only in Westmor- 
land and North Cumberland, but also in the Bristol district, the Forest of Dean, 
and South Wales. 
Foreign Carboniferous. 
From its general similarity to the British deposits we might expect to find 
examples of an algal development in some portion of the Belgian Lower Car- 
boniferous succession. As already mentioned, large masses of encrusting cal- 
careous deposits have been described by Gitrich** from the Visean limestones 
of the Namur basin as Spongiostroma, &c., which, though referred by him to the 
Rhizopoda, may very well be calcareous precipitates deposited by algal influence. 
Many of these deposits are similar to those mentioned above from British rocks. 
No undoubted remains of Calcareous Alge have, however, yet been recorded 
from these Belgian rocks. It may be of interest, therefore, to mention the 
recent discovery by Professor Kaisin, of Louvain, of undoubted algal remains in 
the beds overlying the Psammites-de-Condroz at Feluy on the Samme. The 
form found here resembles Ortonella of the Westmorland rocks, but the tubes 
are much finer, and it may turn out to represent a species of Micheldeania. 
During a recent visit to Belgium I had the pleasure of visiting the Comblain au 
Pont beds, in the Feluy section, with Professor Kaisin, and, although these beds 
have been previously classed as Devonian, I agree with him that they probably 
belong to the base of the Carboniferous and correspond approximately to K of 
the Bristol sequence. In the company of Professor Dorlodot and Dr. Salée, I 
also visited the chief sections of the Visean, and we succeeded in discovering at 
least three horizons at which nodular concretionary structures, probably referable 
to algal growths, occurred. It is pretty certain, therefore, that careful micro- 
scopic investigation of the Belgian rocks will show the presence of Calcareous 
Algze at more than one horizon. 
Again Schubert *? has recently described two new rock-forming genera— 
58 Op. cit. (4°) 59 Jahrb. d. i.-k. geol. Reichsanstalt, 1908, p. 382. 
