The strontium-calcium atom ratio in carbonate-secreting marine organisms 25 



matter and gave an average strontium-calcium atom ratio of 10 / 10 ^ This appears 

 to be in agreement with the finding of McCance and Masters (1937) that ArchiJoris 

 britannica has a high strontium-calcium atom ratio. However, the strontium and 

 calcium content occurs in such low concentrations that a slight experimental error 

 in the determination of either one of the elements markedly affects the atom ratio. 



Class Scaphopoda: The analysis of Scaphopoda was performed on Dentalium 

 which was reported to have a strontium-calcium atom ratio of 2-34 X 10" (Odum, 

 1951 b). The specimen of Dentalium entale (Table I (J)) analyzed by the authors 

 showed an atom ratio of 2-35 x 10-^ 



Class Cephalopoda: Modern Cephalopoda, except Nautilus, usually possess an 

 inner shell. In general, the calcareous inner shells contain more organic matter than 

 the shells of Pelecypoda and Gastropoda. Odum (195 1 b) reported a strontium-calcium 

 atom ratio of 3-87 x 10-^ for a species of Nautilus. The inner shell of Sepia (Table I 

 (J)) was found by the authors to have an atom ratio of 3-74 x 10-^ The chitinous 

 plate of Loligo opalescens was found to contain chiefly organic matter and traces of 

 calcium. 



9. Phylum Bryozoa: The calcium content of Bryozoa studied by previous investi- 

 gators was reported as calcite, but there was little information on the occurrence of 

 other elements. In Table I (K) are the results of analysis of Bryozoa. The strontium- 

 calcium atom ratios averaged 3-41 x 10-^. An appreciable amount of magnesium 

 was present. 



10. Phylum Brachiopoda: The calcareous shells of Class Articulata were reported 

 as containing calcite. Odum (1951 b) found a strontium-calcium atom ratio of 1 -75 x 

 10-* for a species of Terebratula. The other class of Brachiopoda, Inarticulata, 

 consists of apatite, and an atom ratio of 3-60 X 10-* was reported for a species of 

 Crania (Odum, 1951 b). Analyses by the authors showed that Articulata shells 

 (Table I (L)) had strontium-calcium atom ratios ranging from 1 -20 to 1 -57 x 10 *. 



11. Phylum Echinodermata: With the exception of Holothuroidea, the Echino- 

 dermata possess calcium-magnesium skeletons. The body wall of Psolus possesses 

 calcareous plates. The calcium carbonate in skeletons was reported as calcite. Previous 

 investigators reported the following results expressed as percentage of strontium in the 

 ash: Asterias rubens, 0-^%; Marthasterias glacialis, 0-6%; and Ophiocomina nigra, 

 1% (Webb, 1937); Aster ias rubens, 0-15%; Gorgonocephalus eucnemis, 0-2%; 

 Ophiopholis aculeata, 0-2%; and Strongylocentrotus drobachiensis, 0-15% (Vino- 

 gradov and BoROViK-RoMANOVA, 1945). 



The results of analysis of calcareous portions of Echinodermata are shown in 

 Table I (M). All five classes of Echinodermata showed remarkable uniformity in the 

 strontium-calcium atom ratio which could be considered as a constant. 



12. Phylum Chordata: The results of analysis are given in Table I (N). The organ- 

 isms contained an undetermined amount of sand particles and only traces of strontium. 



In Table II are the results of analysis of calcareous materials other than marine 

 invertebrates. The relationship between the strontium-calcium atom ratios of marine 

 Arthropoda and Mollusca and those of fresh water organisms, from the meagre 

 data available for the latter, indicated an analogy: the fresh-water organisms having 

 lower atom ratios. 



