JUNE, 1906. New Forms’ oF CoNCRETIONS—NICHOLS. AQ 
23 ——— Tritonium pompilius,* 0.486 
24 ——  Centhium telescopicum,* 0.189 
BRACHIOPODA. 
25 —— Luangula ovalis,t 3-59 
26.-——_— Terebratula psittacea,* 3 | 0.452 
| VERMES. 
27 ———  Serpula sp. Medtierranean,* 7.044 
28 —— Serpula triqueta. North Sea,* 4.455 
29 —— Serpula filograna,* - 1.349 
: CRINOIDEA. 
30 P6877 Metacrinus rundus, Japan,{ ; See 
CEPHALOPODA. 
31 —— Nautilus pompilius,* Oris 
32 ——  Ossa seprae [Sepia sp.],* 0.401 
| ALGAE. 
33. —— = Lithothamnium nodosum, § Bae 
It may also be noted that Sharples|) when in 1871 he determined 
the phosphate in seven zoanthoid corals observed that traces of 
magnesia were present in all, but made no quantitative determina- 
tions. A. Damour also found small quantities of magnesia in many 
millepores. 
From the above results it appears that the algae, crinoidea, 
vermes and alcyonaria secrete relatively magnesian skeletons, while 
the zoantharia, pelecypoda, gastropoda and cephalopoda secrete 
skeletons which are only slightly magnesian. 
These analyses thus explain why the inner portion of the nodule 
analysed by the author, (p. 45) is less magnesian than the outer part. 
This nodule like many of the others was formed in and around a 
large gastropod. The more highly magnesian corals, serpulae and 
algae of which the nodule is composed are in the central part diluted 
by the less magnesian gastropod material. It is probable that the 
magnesium of the outer part is also somewhat increased by that 
re-solution of the skeletal material which is always taking place. 
If under present conditions corals, etc., secrete skeletons which 
may contain over ten per cent carbonate of magnesia, may they not, 
under palaeozoic conditions, when, as is usually conceded, the sea 
tAnalysis by T. Sterry Hunt: Logan’s Geology of Canada, 1863. The ash analyzed was 61 per 
cent of the whole shell and gave 2.88 per cent Mg O, whence the equivalent Mg CO3 for the entire 
shell has been calculated. 
tCirri and pinnulate arms from an alcoholic specimen. The organic matter is 22 per cent. 
§Analysis by Gumbel; Geikie: Textbook of Geology, p. 482. 
|Sharples: Am. J. Sci., III ser., vol. I, p. 160. 
§ Dana: Manual of Geology, p. 72. 
s 
