PRESIDENTIAL ADDRESS. 455 
Two important genera are usually recognised at the present day as occurring 
in the British Paleozoic 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 spongicides and regarded as referable to the 
Monticuliporoids. 
Nicholson and Etheridge * in 1885 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 J'etradium 
Peachii in 1877, from the Ordovician rocks of Girvan, was also referable to 
Billings’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 ‘ Calcareous 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 tabule.’ * 
At that time Nicholson still considered Solenopora as representing a curious 
extinct hydrozoan, though already, in 1885, Nicholson and Etheridge had 
discussed its possible relationship to the Calcareous Alge. They did not, 
however, consider that there was sufficient evidence for concluding that the 
true structure of Solenopora was cellular, but added: ‘If evidence can be 
obtained proving decisively the existence of a cellular structure in Solenopora, 
then the reference of the genus to the 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 Professor 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 Ordovician 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 Alge, 
and Professor Seward, in Volume I. of his work on Fossil Plants, considers 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 diversity 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 
8 Geol. Mag., 1885, Dec. III., vol. II., p. 529. 
4 Geol. Mag., 1888, Dec. III., vol. V., p. 19. 
5 Op. cit. (8). 
® Geol.*Mag., 1894, Dec. IV., vol. I., p. 145 et seq. 
