48 Field Columbian Museum — Geology, Vol. III. 



organic matter in considerable quantities, so that the ratio of magnesia 



to lime carbonates in the skeletons alone is higher than indicated by 

 the percentages obtained for the dried specimens, which latter percent- 

 ages are the ones in the accompanying table. 



Magnesium Carbonate Content of the Skeletons of Various 

 Marine Calcareous Organisms. 



Analyses by the author in Roman type ; those by other analysts 

 in italics. 



No. Mus. No. Mg C0 3 



ALCYONOID CORALS. % 



'i 377 Eunicea tourneforti, Bahamas, 2.78 



2 381 Plexaurella dichotoma, Bahamas, 2. 11 



3 I sis hippuris* 6.362 



4 Corallium nobile* 2.132 



5 Corallium rubrum, Mediterranean,! 9.32 



6 314 Tubipora musica, Singapore, 3.83 



ZOANTHOID CORALS. 



7 126 Coeloria daedolea, Abyssinia, 0.35 



8 Astraea cellulosa* 0.542 



9 Siderastraea sp., Bermuda,% 0.42 



' BRYOZOA. 



10 1 04 1 Flustra foliacea, California, 1.23 



n Eschar a foliacea * 0.146 



12 1052 Garapholas sp., 3.99 



13 Bryozoan? Bermuda, 5.35 



14 1057 Lithoramnion racemus, Bahamas, 0.65 



15 Myriazoon truncatum,* °-455 



16 Heteropora abrotanoides* 0-352 



17 ■ Frondipora reticulata * 0.596 



pelecypoda. 



18 2879 Teredo gigantea, Indian Ocean, 0.00 



19 Ostrea sp.,% 0.3 



20 Modiola papuana* °-7°5 



21 Pinna nigra, Red Sea * 1.000 



GASTROPODA. 



22 G1331 Vermetus sp., Bermuda, |j 0.35 



* Analysis by J. G. Forchhammer : 1849. Bidrag til Dolomitens Dannelshistorie : Oversigt over 

 det Kongelige Danske Videnskab. 1849, pp. 83 - 96. 

 t Polished material from a necklace. 



X Analysis by L. G. Eakins; Bull. U. S. G. S., No. 228, p. 308. 

 § Analysis by Sharpies ? Dana'- Manual of Geology, p. 72. 

 The incrustation of specimen shown in Plate XXVI, Fig. 5. 



