22 THE INORGANIC CONSTITUENTS OF MARINE INVERTEBRATES. 



In some respects these analyses are unsatisfactory, for they show no regularities of any 

 kind. In only one of them, No. 4, is there exhibited a concentration of magnesium carbonate; 

 in the others the percentage of this constituent is very low. The reason for this decrease of mag- 

 nesia is by no means clear. It is conceivable that the ancient crinoids may have been deficient 

 in magnesia, but it is more probable that the loss is due to alteration, perhaps to the infiltration 

 of calcium carbonate. Such a change would obviously lower the apparent proportion of 

 magnesium carbonate. Several of the crinoids contain noteworthy quantities of ferrous 

 carbonate and manganese — constituents which did not appear in the analyses of the modern 

 species. In No. 8 there is a very strong silicification, 29.11 per cent; bxit the matrix of the 

 specimen contained only 7.55 per cent of silica. Here the infiltration of the impurity seems 

 to be very clear. Some of the deficiencies in magnesia may have been caused by solution and 

 leaching, but calcium carbonate shoidd then have been removed to a greater extent. In short, 

 the fossil crinoids differ widelj^ in composition from the still living species, and in a very irregular 

 manner, and it is worth noting that in three analyses of fossil algae reported by Hogbom " 

 a similar decrease of magnesia appears. It would be easy to speculate on the significance of 

 these differences, but the conclusions so reached would not be entitled to much weight. That 

 the recent crinoids are distinctly magnesian and that the proportion of magnesia is dependent 

 in some way on temperature are two positive results of this investigation. 



2. SEA URCHINS. 



Twelve sea urchins selected for us by Mr. Austin H. Clark and two received from Dr. 

 Hubert L. Clark were analyzed. The species chosen were as follows: 



1. Strongylocentrotus dr6bachiensisO.¥.Mnller. Upernivik, Greenland; latitude 72° 48' N. 



2. Slrongylocentrotus frag'dis Jackson. Albatross station 2946, off southern California; latitude, 33° 5S' 00" N.; 

 longitude, 119° 30' 45" W.; deptli of water, 274..5 metere; bottom temperature, 13.6° C. 



3. Echinarachnius 'par ma IjSiVaaxck. Coast of New England. 



4. Encope califomica Verrill. Galapagos Islands, on or near the Equator. 



5. Lylechinus anamcsus H. L. Clark. Albatross station 2938, off Wilmington, Calif.: latitude, 33° 35' 15" N.; 

 longitude, 118° 08' 30" W.; depth, 86 meters; bottom temperature, 15° C. 



6. Loxechinus albus Molina. Port Otway, Patagonia; latitude, about 46° or 47° S. 



7. Tetrapygus niger Molina. Coast of Peru. 



8. TretociJaris affi7i(S Philippi. Albatross stations 2316 and 2317, off Key West, Fla.; latitude, 24° 25' N.; longi- 

 tude, 81° 47' W. ; depth, 85 meters; bottom temperature, 24° (', 



9. Heterocentrolus mammillatiis Linne. Low or Tuamotu .\rchipelago, .southern Pacific Ocean; latitude, between 

 14° and 24° S. 



10. Encope micropora A. Agjiifsiz. Puerto Viejo, Margarita Bay, Lower California; latitude, 24° 30' \.; longitude, 

 112° W., approximately. 



11. Clypeaster testudinarins Gray. Southern Japan. 



12. Echinus ajfinis Mortensen. Albatross station 2206, between Hatteras and Nantucket; latitude, 39° 35' N.; 

 longitude, 71° 34' SO" W.; depth, 1,919 meters; bottom temperature, 3.6° C. 



Analyses 10-12 by B. Salkover. 



13. Erhinome.tra luciiiiter Linn^. Pigeon Point, Tobago, British West Indies; latitude, 11° 2.5' N.; shoal water, 

 near shore; temperatiu-e, 28° ('. 



14. Mellita sexiesper/nratus Leske. Pigeon Point, Tobago, British West Indies; latitude, 11° 25' N.; shoal water, 

 near shore; ten;perature, 28° C. 



Analyses 13 and 14 by R. M. Kamm. 



" Hogbom, X. C, Neues Jahrb., 1S94, Bund 1, p. 252. 



