196 Dr. Alex. Brown — On Solenopora. 



on one side, and are as thick as the longitudinal walls, while in 

 S. filiformis the transverse cell-walls are straight, and are thinner 

 than the longitudinal walls. Further, in cross section, the cell- walls 

 of S. filiformis are polygonal in form, while the same thing is found 

 to occur very frequently in S. Jurassica. 



Formation and Locality. — Ordovician, Craighead Limestones, 

 Girvan, Ayrshire ; occurring along with Solenopora compacta. 

 (Coll. H. A. Nicholson.) 



6. Solenopora dendriformis, n.sp. 



Under this name I shall describe a species which is found oc- 

 curring along with Solenopora compacta and Solenopora nigra in the 

 limestones of Saak, Esthonia. It presents itself in minute nodules, 

 ovate or spherical in form and dark in colour. Each nodule shows 

 the arrangement of its parts in concentric layers. 



In longitudinal section the cells appear to have a radial arrange- 

 ment ; cell-walls thick and sinuous; transverse walls concave on 

 their peripheral side. The diameter of the cells in each specimen 

 varies very greatly, this being due to the peculiar branching nature 

 of the cells to be presently referred to. The largest diameter is 

 al:)0ut -1-7- mm., but others are very much smaller. The length of 

 the cells is about \ — i mm. or even longer. 



In tangential section the cells appear to branch in all directions, 

 especially horizontally (Fig. 7).. The smaller branching processes 

 are seen cut across in the illustration. 



Fig. 7. — Tang. sect, of Solenopora dendriformis, n.sp., from Esthonia. x 50 d. 



Observations. — The important feature in this species is the extra- 

 ordinary nature of the cells, branching as they do in all directions. 

 Otherwise the nature of the skeleton is much the same as in the 

 species already described. The position and form of its transverse 

 cell-walls show a resemblance to what we find in S. Jurassica and 

 S, nigra. 



Formation and Locality. — Ordovician Limestones of Saak, Esthonia. 

 (Coll. H. A. Nicholson.) 



