ii4 The Ottawa Naturalist. (September 



The general shape of the corallites in this genus, their mode 

 of growth and their internal tabulae, appear to be essentially 

 similar to those of Pycnostyliis^ but in the latter the septa are 

 marginal, well developed, and consist of thin, continuous, longitu- 

 dinal ridges. 



Pycnostylus seems to be most nearly related to Amplexus^ 

 which is usually referred to the Zaphrentidae, and it may be that 

 Aphyllostylus should also be included in that family. 



Aphyllostylus gracilis, sp. nov. 



Corallites slender, averaging about two or three millimetres in 

 diameter ; septal spinules very minute, scarcely visible to the 

 naked eye. 



This genus and species are based upon fragments of colonies, 

 n six small pieces of limestone of Silurian (Upper Silurian) age, 

 rom Stonewall, about thirty-one miles west of East Selkirk, 

 collected by Mr. J. B. Tyrrell in 1897. Each of these pieces of 

 limestone shows both longitudinal and transverse sections of a few 

 contiguous corallites, upon one or more of its recently broken sur- 

 faces. The internal structure of most of these corallites is well 

 preserved, but their mode of branching is nowhere very clearly 

 seen. Two or three similar specimens had previously been col- 

 lected by the writer in 1888 from loose masses of limetone on the 

 banks of the Fairford River, about six or seven miles below the 

 Hudson Bay post at Fairford, Manitoba. 



Ottawa, August 4th, 1904, 



