Nov., 1918] Structure of A gelacrinites and Streptaster 81 



9. The substomial chamber is made by five specialized 

 flooring plates and the posterior peristomial plate mentioned . 

 above. Some species may have two additional plates, one on 

 either side of the anterior first flooring plate. 



10. Cover plates one pair to a floor plate to nearly two 

 pairs (outer) to a floor plate. In the latter case the flooring 

 plate is two primitive floor plates fused. 



11. Stages with one, two and three floor plates are shown. 



12. The probable path of the alimentary canal in the small 

 animal is shown. 



I wish to thank Mr. W. McCord, of Cincinnati, for the 

 privilege of studying his specimens of A gelacrinites. Also 

 Dr. H. L. Clark, of the Museum of Comparative Zoology, 

 Cambridge, Mass., for specimens of the recent Holothurian 

 Psoitis fabricii from Grand Manan. Also Dr. W. H. Shideler, 

 for the use of his material. 



BIBLIOGRAPHY. 



1900. Bather, F. A. Echinoderma. Part III in Lankester's Treatise on Zoology. 



Chapter XII, Edrioasteroidea, pp. 205-211, 8 Figures. 



1908. Studies in Edrioasteroidea. Lebetodiscus new genus for Agelacrinites dicksoni 

 Billings, Geol. Mag. dec. V. 543-550, 4 Figs, and PI. XXV. 



1858. Billings, E. Agelacrinites dicksotii. Canadian Organic Remains, Decade 

 III, pp. 84-85. 



1860. Chapman, E. J. On a new species of Agelacrinites {A. Billingsi). Canadian 

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1901. Clark, J. M. New Agelacrinites. Bull. 49 N. Y. State Mus. 182-198. 7 Figs. 



PI. X. 



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1872. Hall, J. Descriptions of New Species of Crinoidea and other Fossils from 

 Strata of Age of the Hudson River Group and Trenton Limestone. 

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 Museum 1870, 205-232, 3 Figs. PI. 5-8. 



1887. James, U. P. Agelacrinus holbrooki. Reprint from The Pateontologist with 

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1900. Mead, A. D. On the Correlation Between Growth and Food Supply in 

 Starfish. Am. Naturalist 34-397. (Jan.) 



