KCHINODERMS. 



21 



sccins to be correlated with the proportion of niajjjnesia in the crinoids, but tlic chemical ex- 

 planation of the facts is yet to be found. It ma}- have connection with the gaseous content 

 of sea water, carbon dioxide, for example, being more soluble in warm than in cold waters, 

 but this is only a suggestion, which may or may not be fruitful. Tlic same regularity as to 

 temperature also appears in our analyses of alcyonarians. 



FOSSIL CRINOIDS. 



In order to make this investigation more systematic it seemed desirable to analyze a 

 number of fossil crinoids, so as to determine whether any definite and regular changes could be 

 traced in passing from the recent to the ancient organisms. For the material studied we 

 are indebted to the kindness of Mr. Frank vSpringer, who selected the material with great care 

 so as to cover a range of horizons from the Lower Ordovician up to the Eocene. The 10 crinoids 

 chosen are described in the list below, and tlie analyses which follow were made in the same 

 way as those of the modern species: 



1. Fmtacrimis flecadacfylus D'Orhic^ay, stem. Eocene, \'iiicen/,a, luUy. 



2. ^fillericrinlls mexpili/ormi^ Goldhiss, ftem. T'pper Juras.«ic, Kelheim, Bavaria. 



3. Pcntacrinus basaltiformis Miller, stem. Middle Lias (I^ower Jurassic) Breitenbach, Wiirtteiiiberg, Germany. 



4. Encrinus liliij'onnis Lamarck, stem. Triassic, Braunschweig, Germany. 



5. Graphiocrinus magnifais Miller and Gurley. complete cro-mi. Pennsylvanian (upper Carboniferous), Kansas 

 City, Mo. 



6. D(>rynrin>is inikorniv Owen and Shumunl. calyx and r^ieni. Lower jiarl of Burlington limestone, Mi.ssissipiuan 

 (lower Carboniferou.s), Burlington, Iowa. 



7. MegistocritiiL': nodosiia Barris, plates. Middle Devonian, .^liiena, Mich. 



8. Eiicnlijptorr'mHs ctusSlik, plates. Silurian, western Tennessee. 



9. Crinoid sp.?, stem. Trenton limestone. Middle Ordovician, Kirktield, Canada. 

 10. Diaholocriniis vfjspcrali.i White, plate.s and sttsm. Lower Ordo\ i< ian, Tenne.ssee. 



Auuli/si's nf/osxil crinoids. 



licdnccd analy.'ies of fossil crinoids. 



