278 J. F Whiteaves— Occurrence of Siphc-notreta Scotica. 



tinguished. On the other hand I think the change of the preh- 

 nite is primarily into the green diabantite-like mineral and 

 through this into the brown peroxidized substance, and that 

 the instability of the first or protoxide stadium of the sub- 

 stance is the condition of its rapid change from green to brown 

 or black when exposed to the air. Indeed, this is also a strik- 

 ing characteristic of the common diabantite itself, and fresh 

 trap specimens lose their green tint and soon turn brownish- 

 black if exposed to the weather, though the change does not 

 occur with such remarkable rapidity as is the case with the 

 prehnite-diabantite or chlorophseite. Professor Heddle ex- 

 plains the sudden change of color by shrinkage-cracking due 

 to partial dehydration.* 



[To be continued.] 



Art. XXXI.— Note on the Occurrence of Siph, fn-lo S>nh, ,, 



Davidson, in the Utica Formation near Ottawa, Ontario; by 

 J. F. Whiteaves. 



In the spring of 1881, three specimens of a remarkable 

 spinose brachiopod were collected by Mr. J. W. H. Watts, 

 B.C. A., from a band of impure limestone in the Utica Slate at 

 Cumming's Bridge, near Ottawa. These specimens, which Mr. 

 Watts has since presented to the Museum of the Geological 

 Survey of Canada, consist of two perfect examples of the 

 beaked and perforated valve, which is probably the ventral, 

 and of one detached dorsal valve in which the beak is obsolete. 

 Over most of the central area of the sides of the valves the 

 spines are broken off, and where this is the case the surface is 

 marked with pitted imbricating concentric lamellae, the pits 

 representing the fractured bases of the spines. In each case 

 the margins of the valves are densely fringed with a single and 

 continuous row of fine hair-like spines, except immediately 

 upon the beaks. 



Upon examination with an ordinary simple lens it was at 

 once apparent that these specimens are referable to DeVer- 

 nueil's genus Sipkonotreta, and that in most respects they bear 

 a very close resemblance to an English species, the & AngUea 

 of Professor Morris. But the spines of S. Anglica are distinctly 

 stated to be annulated, whereas those of the Canadian speci- 

 mens appeared perfectly smooth when viewed under an achro- 

 matic microscope with an inch and a half objective. 



A few months ago the writer had occasion to send some 

 Canadian fossil Brachiopoda to Mr. Thomas Davidson, F.R.S., 



