imperfectly-known Species of Stromatoporoids. 327 



unfortunately very limited, I am not able to give more than 

 the above very imperfect account of its characters. Its minute 

 structure, as revealed by microscopic sections, is so peculiar, 

 that it could not well be confounded with any other Stroma- 

 toporoid known to me. Its true affinities, however, must 

 remain doubtful until its structural features have been more 

 fully worked out by an examination of well-preserved speci- 

 mens. 



Formation and Locality. Devonian (Corniferous Lime- 

 stone), Kelley's Island, Ohio {coll. Oeol. Survey of Ohio). 



Addendum. 



In describing Clathrodictyon variolar e, Ros., sp., in my 

 ' Monograph of the British Stromatoporoids ' (p. 151), I was 

 not able to refer to the species as occurring in the Palaeozoic 

 rocks of North America. In the collections of the Geological 

 Survey of Canada, however, I find at least two specimens 

 which appear to belong to this widely distributed European 

 type. One of these is a large hemispherical specimen from 

 the Hudson-River formation of Cape Smyth, Lake Huron. 

 The other example, also of large size, is from the Silurian 

 rocks of the Jumpers, Anticosti, and is believed to be the 

 specimen referred to by Mr. Billings in the ' Geology of 

 Canada ' (p. 304, 1863) under the name of Stromatopora 

 concentrica. 



EXPLANATION OF THE PLATES. 



[All the figures of minute structure are based upon photographs, the 

 general scale of enlargement being about ten times the natural size. 

 Where the figures are enlarged further, or are of the natural size, this ia 

 specially stated.] 



Plate VIII. 



Fig. 1. Tangential section of Stromatopora hudsonica, Dawson, sp. Silu- 

 rian, Cape Churchill, Canada. 



Fig. 2. Vertical section of the same. 



Fig. 3. Portion of the surface of an exfoliated lamina of the same, of the 

 natural size. 



Fig. 4. Tangential section of Actinostroma Tyrrellii, Nich., from the 

 Devonian Rocks of Lake W innipegosis, Canada. 



Fig. 5. Vertical section of the same. 



Fig. 6. Tangential section of Syringostroma ristigouchense, Spencer, sp., 

 from the Silurian Rocks of Dalhousie, New Brunswick. 



Fig. 7. Vertical section of the same, similarly enlarged. 



Fig. 8. Part of a tangential section of the same, enlarged about twenty 

 times. 



23* 



