48 



THE IXOKGAXIC CONSTITUENTS OF M.^PJNE INVERTEBRATES. 



In an analysis of Astacus fluvmtilis by O. Biitschli " magnesia wa.s actually determined. 

 We append his analysis, together with our own reduction of it: 



Biitschli's analysis of Astaais. 



In this analysis the low percentage of magnesia is very significant. Astacus is a fresh-water 

 crustacean, whereas the analyses in our series are all of marine forms. In fresh water — the 

 average river water — calciiun is 6 times as abundant as magnesium, but in ocean water mag- 

 nesium is 3i times as abundant as calcium. This difterence in the environment may possibly 

 explain the difference between the fiuviatile and the marine shells, 2.42 per cent of MgCOj in 

 one and 4.84 per cent in the lowest of our determinations. 



One more determination of phosphoric oxide in a crustacean remains to be noted. In the 

 shell of a lobster, Homarus vulgaris, W. H. Hudleston " found .3.26 per cent of P2O5. This is 

 eciuivalent to 7.12 per cent of CajP^Og, or, if the organic matter was about the same in amount 

 as in our analysis of the American lobster, 11.44 per cent in the inorganic portion alone. This 

 is not far from the figure given in our reduced analysis No. 4, namely, 10.91 per cent. 



Although the crustaceans are not of great importance as contributors to the marine sedi- 

 ments, they are more important than appears at a casual glance. A crab or lobster sheds its 

 shell annuall}' and grows a new one, so that an old individual has contributed many times. A 

 single shell might count for little, but when multiplied by a dozen or more the contributions 

 become significant. How significant they may be is for zoologists to determine. 



CALCAREOUS ALG^E. 



The calcareous alga- are so important as reef builders that, although they are not marine 

 invertebrates in the ordinary acceptance of the term, it seemed eminently proper to include 

 them in this investigation. In many places they far outrank the corals in importance, and 

 of late years much attention has been paid to them. To Dr. Marshall A. Howe, of the New 

 York Botanical Garden, we are indebted for a fine series of algae, and to him we express our 

 thanks. 



For the purposes of this research the calcareous &\gie fall into two groups. One of these, 

 of which Lithotha milium is the most familiar example, is highly magnesian; the other, repre- 

 sented by Halimeda, is almost free from magnesia. These groups are best considered sepa- 

 rately, and under the first one we have the following species: 



1. Lithothamnium glaciale Kjellman. Topsail, Conception Bay, Newfoundland; latitude, 4S° N.; longitude, 

 53° W. 



2. Lithothamnium erubescens Foslie. Haingsisi, near Timor, East Indian Archipelago. 



:i. Archxolithothamnium epLiporum. Howe. Point Toro, near Colon, Isthmus of Panama. 



4. LilhophyUum craspedium Foslie. Palmyra Island, in the Pacific Ocean, west of south from Hawaii; latitude, 

 5° 49' N. 



5. Lithophyllwn pallescens Foslie. Bay of La Paz, Gulf of California; latitude. 24° 16' N. 



6. fAthophyllum da^daleum Foslie and Howe. Salinas Bay, near Guanica, Porto Rico; latitude, al)out 18° N. 



7. Lilhophyllum antillarum Foslie and Howe. Culehra Island, Porto Rico; latitude, about 18° 20' N. 



8. Lithophyllum oncodes Heydrich. Coeti\-y Island, in the Indian (Jcean, northeast of Madagascar; latitude, 7° 

 6'S.; longitude, 56° 30' E. 



9. Lithophyllum intermedium Foslie. Fort Clarence, near Kingston, Jamaica. 



10. Lithophyllum pachydermum Foslie. Dollar Harbor, South Cat Cay, Bahamas; latitude, about 25° N. 



« Bulsdili, O., K. (lesell. Wiss. Gottingen Abli., No. 3, 190S. 



" Hudleston, W. H., rieol. Soc. Quart. Jour., vol. 31, p. 376, 1875. 



