320 NOTE ON THE SPECIES MONOHAMMUS. 
to a point at both extremities, with a secondary band with its western extremity 
coinciding with that of the primary and with its eastern extremity immediatély 
under its centre. He further states that the arch was of such extreme tenuity 
‘that stars shone through it with seemingly no diminution of their brilliancy. 
The chief points of difference between the phenomena at the two places con- 
sist in the tenuity of the luminous matter as seen at Peterborough, the circum- 
stance that there the streamers proceeded from instead of into the arch, as at 
Toronto, and that Mr. Clementi makes no mention of the apparent transfer of the 
luminous matter which here formed the chief peculiarity. 
Luminous arches extending through the zenith in a direction perpendicular 
to the meridian, though not an ordinary accompaniment of the aurora, have 
been noticed before at Toronto and elsewhere, though rarely attended with the 
peculiar appearances which marked the display of April 9th. 
G. T. K. 
NOTE ON THE SPECIES MONOHAMMUS. 
To the Editor of the Canadian Naturalist. 
In the December number of the Canadian Naturalist Mr. Billings has described 
some of the pine-boring beetles of Canada, of ‘the ‘genus Monohammus, and 
-mentions that the M. fitillator is cited by ‘Mr. Couper and Mr. Ibbetson ‘as 
occurring at Toronto, but is of opinion that the insect described is the M. con- 
Fusor. 
I can confirm this idea of Mr. Billings, as the insects in my own collection 
and in that of Mr. Ibbetson were named on reference to Harris’ work. The 
description agrees very closely with the reddish brown specimens mentioned by 
Mr. Billings as having been obtained from Toronto, where from my own observa- 
tions they seem to be much more common than those of ‘a cinereous tint. 
Moreover the drawing of Monohammus titillator in Olivier’s work agrees very 
well with these specimens. Those in my collection are mostly of the same size 
as the M. confusor and generally a little more robust, but ‘are probably only a 
variety. The M. scutillatus is moderately common about Toronto, but the 
M. marmoratus quite rare ; the latter easily distinguished by its smaller size, its 
rugosely punctured thorax, and the elytra mottled with brown and grey. 
In my collection there is also a crippled specimen very like M. scutillatus but 
the elytra are covered with large white spots, in this respect resembling Leconte’s 
_ M. fatuor, which however is now referred to M. marmoratus, 
In the recent edition of Harris’ work the name titillator is still employed. 
i H. C. 
ON GROUND-ICE, OR ANCHOR ICH, IN RIVERS. 
' BY PROFESSOR JAMES THOMPSON. 
In this paper the author described the two principal modes of growth of ‘ice, 
in still water and in running water. In still or slowly moving water the ice 
forms itself'as a crust on the surface, because, as the water cools from about 
