254 BRITISH UPPER SILURIAN FENESTELLID-^. 



marked than the preceding, is the species I have described as 

 Fenestella reteporata. In size and outline the species is decidedly 

 Betepora in character. It has none of the straight lines and general 

 •uniformity of structure which are so characteristic a feature of the 

 Fenestellidse. Instead of this we have irregular interstices, and 

 fenestrules of all shapes. The dissepiments, however, show most 

 markedly the character of Betepora. Not on all, but on some of 

 them, it is most difEcult to distinguish between the dissepiment and 

 interstice, so near do they approach in character the anastomosis of 

 the branch, which is the distinguishing feature in Betepora. The 

 likeness is further assisted by the occurrence here and there of cells 

 on the dissepiments. These latter features are not so marked or 

 persistent as to cause any doubt as to its being a true Fenestella, 

 while they indicate clearly the direction whence the disturbing in- 

 fluence came. 



I desire to express my obligations to Professor Hughes of Cam- 

 bridge, and also to the officers of the Geological Society, for much 

 assistance in examining the type specimens under their charge. 



EXPLANATION OF PLATE XI. 



Fig. 1. Fenestella reteporata, Shrubsole. A specimen of the natural size in the 

 Woodwardian Museum, Cambridge. 

 1 a. Obverse view, X 12 diameters. 

 1 b. Reverse view, X 12 diameters. 



1 c. Ring of pits, within cell-mouth. 



2. Fenestella lineata, Shrubsole. Portion of obverse surface, X 12 dia- 



meters. Only partially weathered from matrix. 



2 a. Reverse face, X 12 diameters. 



3. Fenestella intermedia, Shrubsole. From the cabinet of G. H. Morton, 



F.G.S. Portion of obverse surface, X 12 diameters. 



3 a. Reverse face, X 12 diameters. 



Discussion. 



The President remarked upon the value of this communication, 

 and upon the service done by the author in reducing the number of 

 supposed species of Polyzoa in the Carboniferous and Upper Silurian 

 rocks. 



