380 H. How on the Comparative Composition of Shells. : 
Museum. The limestone is Nova Scotian. The first a is 
that “of the shell of the Periwinkle (Litorina litorea). The 
sults obtained were these: - 
a, Il. Mean. 
© 54°551 54378 54°464 
ar - Se REO U he a ean 821 
Sulphuric acid, - 0-282 0°283 0°282 
rganic cr - - 2°010 2°040 2-025 
Sand and silic - - 0-164 ae 0164 
Phosphoric sa, oe se ue ek 0-001 
99°757 
@ Containing 0-07 nitrogen. 
The analysis of the shell of the oyster (Ostrea edulis) gave, 
I. 
1 
- - - 53°368 seer 
nic acid, - . . - - 40-600 
Sulpburicaeid,- - - = - 0809 0°800 
deg matter,? - - . - 3478 3°170 
and and silica - - - : 1°495 aoe 
Phosphoric acid, - - + - + 0106 sess 
Sesquioxyd of iron, - - - = = 0-039 eee 
99°895 
6 Containing 0'155 nitrogen. 
On comparing these oe with the preceding, we geet 
a great increase in the amounts of sulphuric acid, phosphor! 
acid, and, apa in organic breaiyi in which, moreover, the 
nitrogen is mu 
The analysis ea ‘ahd “shell ery the Mussel (Mytilus edulis) gave: 
Lim - - - - §2°862 
Carbonic acid, s - - - - 41°020 
Sulphuric acid, - - - ~ . : 
Organic matter, - - . - - 5-020 
Sand and silica, - - - - - 
Phosphoric acid, . ‘ ‘ Fs FA 048 
yd of iron, . e158 & - - 036 
99640 
comparing with the foregoing we observe again increased 
ergatic matter, while sulphuric and phosphoric acids are much 
as in Litorina. 
The Silurian fossil was cca  heaae It gave, 
Lime - ‘ - 64:02 
Carbonic acid, - - - é = 4.79 
Sulphurie acid, “ - « " “ - O65 
ee same, - - - - si 161 
ilic - - - - . me 
Phosphoric acid, - - . - - 014 
Sesquioxyd of iron, - - - - - 0-26 
99°95 
_ prin 28 here shown between this brachiopod shell and 
that of the univalve Litorina is very great, We ould rather 
