ON THE INORGANIC CONSTITUENTS OF THE SKELETONS 

 OF TWO RECENT CRINOIDS. 



By Austin Hob art Clark, 



Assistant Curator, Division of Marine Invertebrates. 



Dr. Chase Palmer, of the U. S. Geological Survey, has recently been 

 so kind as to make for me, under the direction of Prof. F. W. Clarke, 

 analyses of the chief inorganic constituents of the skeletons of two 

 recent crinoids, taken under very different conditions of temperature 

 and light, but at nearly the same depth, and consequently at nearly 

 the same pressure. 



While there has been a considerable amount of work done in regard 

 to the determination of the elements of the skeleton of many marine 

 animals, more particularly corals and mollusks, there is only a single 

 record to be found among the recent crinoids. In 1906 Mr. Henry 

 W. Nichols^ analyzed some pinnulate arms from a specimen of Meta- 

 crinus rotundus from southern Japan (probably Sagami Bay), and he 

 found that the skeleton contained 11 per cent of magnesium carbon- 

 ate, a greater proportion than had been detected in the skeleton of 

 any marine animal previously examined. 



The material submitted to Doctor Palmer consisted of pinnulate 

 arms of Metacrinus rotundus from the Eastern Sea and of Heliometra 

 maxima from the Sea of Okhotsk. Both specimens were air dried 

 from alcoholic examples collected by myself in 1906. 



METACRINUS ROTUNDUS. 



Metacrinus rotundus P. H. Carpenter, Trans. Linn. Soc. (Zool.), (2), vol. 2, 

 1885, p. 436, pi. 50; pi. 52, figs. 1-7. 



Locality.— Albatross station 4934; lat. 30° 58' 30" N.; long. 130° 

 32' 00" E. (Sata Misaki light bearing N. 77J° E., 7 miles distant), in 

 the Eastern Sea off Kogoshima Gulf; depth, 152-103 fathoms; bot- 

 tom temperature, about 56° F.; surface temperature, 84° F.; surface 

 density, 1.02355. 



Tliis is the same species as that analyzed by Nichols. It is probable 

 that tlie depth is somewhat greater and the temperature slightly less 



"Field Columbian Museum, Geol. Ser., vol. 3, 1906, p. 49. 



Proceedings U. S. National Museum, Vol. 39— No. 1795. 



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