LT2 
NATURE 
[SEPTEMBER 25, 1913 
not until the researches of Phillipi were published in 
1837 that certain calcareous deposits were discovered 
to be directly due to the growth of living forms of 
lime-secreting alga, it is not surprising that, only in 
comparatively recent years, has the importance of the 
fossil forms as rock-builders in past geological forma- 
tions been recognised. 
The original genera established by Phillipimnamely, 
Lithothamnion and Lithophyllum—are known now to 
have a wide distribution in the present seas, and it is 
therefore natural that it was members of these groups 
which were the first to be recognised in a fossil state 
in Tertiary and, subsequently, in upper cretaceous 
rocks. 
Thus in 1858, Prof. Unger of Vienna showed the 
important part played by Lithothamnion in the con- 
stitution of the Leithakalk of the Vienna Basin, while 
seven years later Rosanoff contributed further to our 
knowledge of tertiary forms. In 1871 Giimbel pub- 
lished his monograph on the ‘so-called Nullipores 
found in limestone rocks,’’ with special reference to 
the Lithothamnion deposits of the Danian or 
Maestricht beds. Since then Lithothamnion has also 
been reported from Jurassic rocks, and even from 
beds of Triassic age, though in the latter case, at all 
events, the reference to this genus appears to require 
confirmation. In this country the recognition of fossil 
calcareous algz dates from a considerably later 
period. It will be best first to review the chief genera 
which appear to be referable to the calcareous alge, 
and afterwards to show the part they play as rock- 
builders in the different geological formations. 
Two important genera are usually recognised at the 
present day as occurring in the British Palaeozoic and 
Mesozoic rocks—namely, Solenopora and Girvanella 
—and to these I propose to add Wethered’s genus, 
Mitcheldeania, together with certain new forms from 
the Carboniferous rocks of the North of England, 
which appear also to be referable to this group. 
Solenopora. 
This genus was first created by Dybowski in 1877 
for the reception of an obscure organism, from the 
Ordovician rocks of Esthonia, which he described 
under the name Solenopora spongioides, and regarded 
as referable to the Monticuliporoids. ‘ 
Nicholson and Etheridge in 1885 (Geol. Mag.., 
p. 529) showed that the form described by Billings 
in 1861 as Stromatopora compacta, from the Black 
River limestones of North America, was in reality 
Dybowski’s genus Solenopora, and in all probability 
was specifically identical with the form from Esthonia. 
Moreover, they considered that the organism they 
themselves had described under the name of Tetradiwm 
Peachii in 1877, from the Ordovician rocks of Girvan, 
was also referable to Billing’s species, though perhaps 
a varietal form. Thus Solenopora compacta was 
shown to have a very wide distribution in Ordovician 
times. 
Nicholson in 1888 defined the genus as including 
‘“Caleareous organisms which present themselves in 
masses of varying form and irregular shape, com- 
posed wholly of radiating capillary tubes arranged in 
concentric strata. The tubes are in direct contact, 
and no coenenchyma or interstitial tissue is present. 
The tubes are thin-walled, irregular in form, often 
with undulated or wrinkled walls, without mural 
pores, and furnished with more or fewer transverse 
partitions or tabulze.”’ * 
At that time Nicholson still considered Solenopora 
as representing a curious extinct hydrozoon, though 
already, in 1885, Nicholson and Etheridge had dis- 
cussed its possible relationship to the calcareous alge. 
3 “Geol. Mag., 1888, Dee. 3, vol. v, p. 19. 
NO. 2291, VOL. 92] 
They did not, however, consider that there was 
sufficient evidence for concluding that the true struc- 
ture of Solenopora was cellular) but added: “If 
evidence can be obtained proving decisively the exist- 
.ence of a cellular structure in Solenopora, then the 
reference of the genus to calcareous algz would 
follow as a matter of course." * 
In 1894 Dr. A. Brown investigated more fully the~ 
material which had been placed in his hands by Prof. 
Nicholson, and gave an account of all the forms 
referable to Solenopora known at that date. 
To those already recorded, he added descriptions of 
four new species from the Ordovician rocks—namely, 
S. lithothamnioides, S. fusiformis, S. nigra, and 
S. dendriformis, the two latter being from the Ordo- 
vician rocks of Esthonia. 
In the same paper also he published for the first 
time a description of a new species of Solenopora from 
the Jurassic rocks of Britain, to which Nicholson, in 
manuscript, had already assigned the name of 
S. jurassica, though, as will be pointed out later, it 
is probable that two distinct forms were included by 
Brown under this name. 
This record of Solenopora from the lower Oolites 
of Britain extended the known range of this genus, . 
for the first time, well into the Jurassic period. In 
this paper Brown first brought forward good evidence 
for removing Solenopora from the animal kingdom, 
and placing it among the coralline alga, and Prof. 
Seward, in Vol. i. of his work on fossil plants, con- 
siders that there are good reasons for accepting this — 
conclusion. 
At the time of the publication of Dr. Brown’s paper, 
and for some years afterwards, the only formations. 
in which Solenopora was known to occur were the 
upper Ordovician and the lower Oolites. The diver- 
sity of forms, however, met with in the Ordovician 
rocks, and their widespread distribution, pointed to 
the probability of the existence of an ancestral form 
in the older rocks, while it also appeared incredible 
that no specimens of intervening forms should have 
been preserved in the rocks representing the great 
time-gap between the Ordovician and Jurassic forma- 
tions. 
In this connection Prof. Seward remarks*: “It is 
reasonable to prophesy that further researches into 
the structure of ancient limestones will considerably 
extend our knowledge of the geological and botanical 
history of the Corallinaceze.” This prophecy has been 
amply fulfilled, especially as regards this particular 
genus, and recent discoveries go far towards filling 
the previously existing gaps in our knowledge of the 
vertical distribution of this interesting genus. 
Thus the recent detection in the lowest Cambrian 
rocks of the Antarctic continent of a form which 
appears to be referable to this genus enables us to 
trace the ancestry of Solenopora back almost to the 
earliest rocks in which fossils have yet been discovered, 
while the gap in the succession which previously 
existed between the Ordovician and Jurassic forms 
was decreased by the description in 1908 by Prof: 
Rothpletz of a new species Solenopora Gothlandica, 
from the Silurian rocks of the Far6e Islands in Got- 
land.¢ A large number of deposits, however, still 
remained, between the Gotlandian and lower Jurassic 
beds, from which no example of Solenopora had so 
far been recorded. 
The identification, therefore, a few years ago, by 
Dr. G. J. Hinde, of examples of this genus from 
among the nodules I had collected from the Shap 
dolomites, is of considerable interest, as the presence 
of Solenopora in the lower Carboniferous rocks of this 
4 ‘Geol. Mag., 1885, Dec. 3, 2, p. 534. 5 Of, cit., p 190. 
_ § “Kungl. Svenska, Vets. akad. Handl." Bd. 42, No. 5, 1908, p. 14, pl. 
iv., PP. 1-5. . 
