ACTINOCEINID^. 593 



PHYSETOCRINUS M. and W. 



1869. Meek and Woethen (Subgenus of Strotocnims) ; Proceed. Acad. Nat. Soi. Phila., p. 158 ; also 1873, 



Geol. Kep. Illinois, Vol V., p. 349. 

 1881. W. and Sp. ; Revision Palfeocr., Part II., p. 155 (Proceed. Acad. Nat. Sci. Phila., p. 329). 

 1889. S. A. MiLLEB. ; North Amer. Geol and Palseont., p. 269. 



Arrangement of the plates up to the distichals as in Actinocrimcs ; but the 

 anus located within the tegmen, not at the end of a tube. The calyx dis- 

 tinctly lobed. The arms arranged in groups, and given off from the two 

 main divisions of the rays alternately from opposite sides. But, contrary to 

 the case in Actinocrinus, each order of brachials, from the costals up, consists 

 of but a single plate, which is axillary, and supports on one side an arm and 

 upon the other a brachial of a higher order. Arms biserial. Interbrachials 

 numerous, and in contact with the plates of the disk. Ventral disk depressed 

 at the summit, phcated around the margin, and generally composed of small, 

 irregular pieces. Anus excentric. Column round. 



Distribution. — Only known from the Burlington group in America, but it 

 apparently occurs also in the Mountain limestone of Ireland. 

 Type of the genus : Physetocriniis ventricosus. 



Remarks. — Zittel makes Physetocrinus synonymous with Strotocrinus, and 

 the latter a subgenus of Actinocrinus. 



Physetocrinus ventricosus (Hall). 

 Plate LXIII. Fig. 6, and Plate LXIV. Figs. 1, B, 3, 4, 5, 6, 7, and 8a, I. 



1838. Actinocrima ventricosus — Hali,; Geol Rep. Iowa, Yol I., Part II., p. 595, Plate 11, Figs, da, b. 

 1873. Fhysetocrimis ventricosm — Meek and Worthen; Geol. Rep. Illinois, Vol. V., p. 349. 

 1881. Phi/setocrimts ventricosus — W. and Sp. ; Revision Pateocr., Part 11., p. 157. 



Syn. Actinocrinus subventricosus McChesnet; 1860, New Pal. Foss. p. 21 also 1869, Chicago 

 Acad. Sci., Vol. I., p. 16, Plate 4, Pig. 6. 



Syn. PhysetocTinus subventricosus — Meek and Woethen; Geol. Rep. Illinois, Vol. V., p. 349. 



Syn. Actinocrinus ventricosus var. cancellatus. Hall ; 1861, Prelim. Descr. Pal. Foss., p. 3. 



Syn. Actinocrinus ventricosus, var. intemodius Hall ; 1861 Bost. Joum. Nat. Hist., p. 278. 



Syn. Actinocrinus ventricosus, var. reticulatus Hall; ibid., p. 279. 



Of more than medium size. Calyx generally as wide as high, somewhat 

 higher in 3'oung specimens. Dorsal cup basin-shaped ; the sides convex below, 

 more rapidly spreading from the top of the distichals ; the arm bases pro- 

 jecting, deeply grooved between the rays and their main divisions, and 



slightly between the individual arms. Ventral disk hemispherical, varying 



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