270 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



Glyptocrinus decadactylus Hall. 

 Plate XX. Figs. Jfa-e and Plate XXI. Figs, Jjm^ h. 



1847. Hall ; PalfEont. N. Y., Vol. I., p. 281, Plate 11, Kgs. l«y and Plate 78, Pigs. \a-u, 



1873. Meek; Paljsont. Ohio, Vol. I., p. 30, Plate 2, Figs. 5«, b. 



1879. Zittel ; Handb. d. Pala30iit., Vol. L, p. 375, Pig. 262. 



1881. W. and Sp. ; Revision Palajocr., Part II., p. 188 (Proceed. Acad. Nat. Sci. Pliila., p. 362). 



1883. S. A. Miller; Journ. Cincin. Soc. Nat. Hist., Vol. VI., p. 220, Plate 11, Pig. 1. 



Calyx obconical, somewhat higher than wide ; the interradial and inter- 

 distichal spaces a little flattened, giving a cross-section pentagonal through 

 the costals and decagonal through the distichals. Surface beautifully orna- 

 mented with radiating angular ridges ; those following the rays to the arms 

 a little the largest and most prominent. Other ridges pass sideways from 

 the centre of the plates, meeting with similar ridges from the interbrachials, 

 which divide the surface into numerous triangular impressed areas. 



Basals small, their width at the top greater than the height. Eadials 

 heptagonal, larger than the basals, and as wide as long. First costals a little 

 smaller than the radials, and hexagonal ; the second as large as the first, but 

 angular above. Distichals two, comparatively large. Arms twenty, simple, 

 rather stout, cylindrical. The four lower plates, which in large specimens 

 are incorporated into the calyx, are elongate, but decrease in length upward ; 

 their upper and lower faces being parallel, the succeeding free plates slightly 

 cuneate. Pinnules long, closely arranged ; the proximal ones given off from 

 the third palmars, there being none from the distichals. Interbrachials 

 numerous, gradually decreasing in size; arranged in ten to twelve ranges: 

 1, 2, 2, 2, etc.^ at the regular sides, sometimes with three plates in the second 

 row. Anal side having three plates in the second and succeeding rows ; the 

 plates of the median series longitudinally arranged, and covered by a ver- 

 tical ridge similar to the ridges along the rays. Interdistichals in four to five 

 rows, the interpalmars in three ; the former arranged : 1, 2, 2, 2, 2 ; the 

 latter placed in a single longitudinal row. Ventral disk slightly convex, 

 composed of irregular pieces with a small prominence in the centre. The 

 plates are small, and gradually decrease in size outward, those along the 

 margin being quite minute, and enclose some of the " Saiimpldttclien'' The 

 latter, which are also frequently preserved upon the arms and pinnules, con- 

 sist of two very small irregular rows of pieces. Anus subcentral, at the 

 upper end of a protuberance. Column round, of moderate size, the nodal 

 joints a little the widest ; axial canal rather large and pentalobate. 



