286 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



Specimens small. Calyx obconical to subglobose ; generally with promi- 

 nent ridges along the radial and anal plates ; the surface densely covered 

 with very fine striae or small granules. 



Basals three, large, unequal, forming a more or less deep cup ; two of 

 the plates equal, the other one half smaller. Eadials very large ; their upper 

 corners but slightly truncated by the interbrachials. Costals two, small; 

 rarely more than one third the size of the radials, and in some species still 

 smaller. Of the distichals generally only the first plate takes part in the 

 calyx, but occasionally also the second. Arms ten, long, biserial, and simple 

 throughout. Interbrachials few. Anal area much the widest and quite 

 distinct. It has three plates in the first row, of which the middle one is 

 placed against the sloping upper faces of the two posterior radials; while 

 the two smaller ones at the sides, together with the first costal, occupy the 

 upper face of the plate, in a similar manner as the corresponding plates of 

 the PlatycrinidaB, except that those of Macrostylocrinus do not extend beyond 

 the limits of the dorsal cup. The middle or anal plate is generally followed 

 by one or two other anals, longitudinally arranged. Ventral disk low; com- 

 posed, so far as observed, of small irregular pieces. Column round ; axial 

 canal small. 



Distribution. — Eestricted to the Niagara group of America. 



Type of the genus : Macrostijlocrimis ornatus Hall. 



Eemarks. — This genus differs from all other Melocrinites in the number 

 of basals, and in having in the anal interradius three plates in the first row, 

 while the others have but one. The anal side of Hall's diagram on page 130 

 of the 28th Eep. N. Y. State Museum is incorrectly given, and it appears 

 from the description that Hall was not aware that in Macrostylocrinus the 

 arrangement of plates in the anal interradius differs from that of the other 

 sides. The basals in that diagram are represented as equal, while in fact 

 they are unequal, two of them being larger than the third. 



Shumard regarded this genus as identical with Ctenocrinus Bronn, from 

 which it differs in the construction of the anal interradius — the latter 

 having but one plate in the first row — ^and also in the number of basals. 



Macrostylocrinus ornatus Hall. 

 Plate XXIII. Figs. 8a, &, c. 



1851. Macrostylocrinus ornatus — Hall; Palseont. N. Y., Yol. II., p. 204, Plate 46, Pigs. ^a-g. 

 1866. Ctenocrimis ornatus — Shumard; Trans. Acad. Sci. St. Louis, p. 361. 

 1881. Macrostylocrinus ornatus ■ — W. and Sr. j Revision Palseocr., Part IL, p. 103. 



