Prof. H. A. Nicholson—Organisms in Paleozoic Limestones. 21 
We recognized its occurrence in the Trenton and Black River Lime- 
stones of North America, in limestones of corresponding age in 
Esthonia (“ Jewesche Schichten”’), and in the Ordovician limestone 
of Oraighead, near Girvan, in Ayrshire. To the facts previously 
recorded with regard to the range of this remarkable fossil, I can 
now add some further information of interest. Thus my friend Prof. 
Lapworth has recently submitted to me a number of examples of 
this species, of unusually large size, which he has collected in the 
“Hoar-Edge Limestone” of Shropshire. This discovery has the 
effect of extending the known range of Solenopora compacta in 
Britain from the Ordovician area of Ayrshire to that of the classical 
district of the West of England. Again, I find that the fossils 
described by Mr. S. A. Miller, from the Cincinnati group of North 
America under the name of Stromatocerium richmondense (Journ. 
Cincinnati Soc. Nat. Hist. vol. v.) are in part referable to Solenopora, 
and are undistinguishable from S. compacta, Bill., sp. Mr. H. O. 
Ulrich has been kind enough to furnish me with a number of speci- 
mens from the Cincinnati group of Indiana, which he regards as 
referable to the so-called Stromatocerium richmondense. These speci- 
mens are in the form of small irregular calcareous masses, very 
closely resembling one another in general appearance, but differing 
so far that, when broken across, some show a conspicuous composition 
out of concentric layers, while others are more compact and uniform 
in texture. In point of fact, the specimens, in spite of their apparent 
similarity, are not all the same. Some of them are referable to 
Solenopora compacta, Bill.; others are referable to a species of 
Girvanella (= Strephochetus, H. M. Seeley) ; while others are com- 
posed of both these organisms growing in superimposed colonies. 
SoLENOPORA ? FILIFORMIS, n. sp. Fig. 4. 
In the Ordovician limestone of Craighead, near Girvan, there 
occurs a fossil which I may provisionally describe under the above 
name, and which is associated with the preceding in the formation 
of the limestone. It is often present in great abundance in the lime- 
stone, but its internal structure is commonly much obscured, or even 
destroyed by crystallization. It presents itself sometimes in the 
form of small rounded or irregular nodules, or, at other times, as 
lobate or ramified masses of considerable dimensions. Viewed with 
a powerful magnifying glass it appears to be quite compact, or 
obscurely fibrous; but when examined microscopically, it is seen 
to be composed of exceedingly minute capillary radiating tubes 
disposed in concentric strata. The tubes are thin-walled, regularly 
prismatic in shape, without mural pores or radiating septa, but 
furnished with numerous transverse partitions or “tabule ” (Fig. 4). 
The average diameter of the tubes is about #; of a millimétre. 
Increase of the tubes appears to take place by fission, but the tubes 
do not exhibit inward septiform processes, such as are so character- 
istic of the cross-sections of the tubes of Solenopora compacta. 
I have some doubts about the reference of this fossil to the genus 
