HH, How on the Comparative Composition of Shells, 379 
equal length, it will be corrected for the inequality of the months 
we take 
=A,+'0041 A,+A, sin (exe, —0° 46’). 
This rule may be expected to hold good for extra-tropical cli- 
mates generally. 
The corrections due to the remaining constants, A,, e,, A,, 
e,, &c., seem to be dependent on local peculiarities of tempera- 
ture, and not subject to any simple and general laws. 
The utility of any system of representing climates by equa- 
tions of curves must of course depend much upon the accuracy 
of the representation. Enough has been done to show that 
equations derived from monthly means will fail to determine 
the annual mean and the “date of phase” with any considera- 
ble degree of accuracy unless allowance is made for the inequal- 
ity of the months. It is probably safe to assert that the method 
of mean months will give results of a higher degree of exacti- 
tude than any other method which does not employ more than 
twelve temperatures to determine the values of the constants, 
Dee, 1865. 
Art. XLVI.—On the comparative composition of some Recent 
Shells, a Silurian Fossil Shell and a Carboniferous Shell Lime- 
stone; by Prof. How, D.C.L., University of King’s College, 
Windsor, Nova Scotia. 
THE analyses of shells here given were originally made as 
part of an investigation which it was proposed to institute into 
the composition of various recent as compared with that of well 
anal fossil molluscous shells. The enquiry was set on foot 
y Dr. Lyon Playfair, at that time Professor of Chemistry in 
periments made. I now communicate the analyses which, with 
Were scrupulously cleaned from their inhabitants. When the 
animal matter could not be entirely removed in the fresh state 
it was allowed to putrefy till it could be separated. The Silurian 
fossil shell was obtained from the collection in the British 
