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ny 696 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
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{i scarcely one third the width of the plates, and extending but little inward. 
: | Costals subtriangular, the sloping upper faces concave, the angle sharp. 
. Distichals nearly as long as wide, not in contact laterally, each one giving 
We | off two arms. Arms four to the ray, rather delicate from their origin, com- 
7. | posed of cuneate pieces, which interlock from the fourth or fifth piece and 
| become biserial; their joints are long, and all more or less constricted across 
| the middle. Ventral disk moderately high, hemispheric; its plates numer- 
al ous. The interambulacral pieces of the regular sides consist of three and 
lUlLhLae two plates, so far as observed, of which the middle one of the first row is 
| large; the anal side has five in the first range, followed by numerous very 
mC small, convex pieces, forming a large, well defined protuberance, which 
' { | ii | encloses the anus. Orals and ambulacral plates not visible in the specimens. 
T | Horizon and Locahty. — Lower Burlington limestone, Burlington, Iowa. | 
fl Type in the Museum of Comparative Zodlogy. 
| } Remarks. — Hall’s P. clytis is a young specimen of P. scobina M. and W.., | 
4 H and the former name should have priority if the form had been satisfactorily : 
| | | described; but unfortunately the short preliminary notice of it which Hall | 
K | | i gave is insufficient for specific identification, and we must in justice to Meek 
| and Worthen accept their name. MHall’s more elaborate description, which 
appeared in 1862, is misleading, for he describes the species as having only 
1 i three arms to the ray, in which it would be unique among all Platycrinide. 
a a Hall’s type was imperfect, and the arms, according to the figure, are uni- 
| i serial throughout, as in all young specimens of Platycrinus. 
| . Platycrinus parvinodus Hatt. 
| a Plate LXVUIII. Figs. 6a, b. 
| | | | 1861. Hati; Descr. New Spec. of Crinoids, p. 17. 
og i 1881. W. and Sp.; Revision, Part IJ, p. 73 (Proceed. Acad. Nat. Sci. Phila., p. 247). 
b | | 3 A small species. Dorsal cup wider than high, broadly caliculate, slightly 
ie . obconical at the lower end, the sides evenly convex. Plates extremely thin, 
| marked by irregular lines of sharp, very small nodes, passing from the radial | 
facets to the lower angles of the plates, and from the columnar facet to the | 
upper angles of the basal cup, with a few similar nodes irregularly scattered 
| Et upon the surface. The nodes in some specimens are only visible with 
| |i a magnifier. Basi-radial and interradial sutures on a level with the general 
! a surface of the plates. | 
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