24 



THE INORGANIC CONSTITUENTS OF MARINE INVERTEBRATES. 

 Analyses of Heteroceatrutus maminillatus. 



Sholl. 



SiOo 



(AI,Fe).,03. 

 MgO. .."... 



CaO 



SO3 



P2O5 



Ignition . . . 



CO., needed 



Organic matter, etc. 



0. 02 



.13 



5. 21 



43.fi0 



.61 



Trare. 



49.62 



99. 1.9 



39.66 



9.96 



Denial 

 |)vramid. 



0.02 



.08 



0. 50 



46.02 



.58 



Trace. 



47.00 



White 

 spines. 



0.05 

 .13 



3.74 



48. 26 



.29 



Trace. 



46.46 



99.20 



42. 89 

 4. 11 



98. 93 



41.77 



4.69 



Heduced analyses of Heleroeentrolns iiiammillatiis. 



SiOj 



(Al,Fe),03. 

 MgCO,."... 



CaCOa 



CaSO, 



CaaPA--- 



100. 00 



100.00 



Red 



spines. 



0.05 



.26 



4.47 



47.72 



.78 



Trace. 



45. 99 



99.27 



41. 49 



4.50 



0.05 

 .28 



9.86 

 88.43 



1.38 

 Trace. 



100.00 



From these analyses we see that the inorganic constituents of Heteroccntiolus are not 

 uniformly distributed. The shell and teeth are alike and are rich in magnesium carbonate; the 

 coarser spines are much less magnesian. The composition of the entire skeleton, if it can be 

 called so, would probably be somewhere near that of the red spines alone, onh- a little higher 



A similar example is offered by No. 8, Tretocidaris. In the specimen analyzed the shell 

 and spines were taken separately, but the spines were dead when the urchin was collected. 



The analyses are as follows: 



Analyses of Tretocidaris ajjinis. 



Actual analyses. 



SiOj 



(Al.Fe)^ 



MgO 



CaO 



SO3 



P,0, 



Ignition 



('O2 needed 



Organic matter, etc 



Shell. 



0.11 



.15 



4.02 



45.80 



.57 



Trace. 



48.32 



98.97 



40.09 



8.23 



Spines. 



0.53 



.14 



2.07 



49.79 



(?) 



Trace. 

 46.28 



98.81 

 41.40 



4.88 



Reduced analyses. 



SiO, 



(Al,Fe).,03 

 MgCOj.... 



CaCOa 



CaSO^.... 

 (XPA-- 



Shell. 



0.12 



.16 



9.30 



89.35 



1.07 



Trace. 



100. 00 



Spines. 



0.56 



.15 



4.63 



94.66 



(?) 

 Trace. 



100. 00 



Here again the spines are lower in their content of magnesia than the shell. 



In two of the analyses, Nos. 4 and -5, large percentages of silica and sesquioxides appear. 

 These are due to inclosed or adherent sand and mud, which were visible in the specimens but 

 not readily removable. On rejecting these impurities and recalculating to 100 per cent, the 

 percentages of magnesium carbonate became 1 1 .43 and 8.59, respectively. Similar corrections to 

 the other analyses are negligible. Mter making these corrections and assuming the percentages 

 found for the shell rather than the spines in Nos. 8 and 9, the next table has been constructed. 

 If, however, the composition of the entire Heterocentrotus should be taken, it would fall below 

 Encope californica. 



