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O24 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
the three plates above succeeded by three plates, and numerous other plates 
irregularly arranged in rows of from five to six pieces each, which grow 
sinaller as they approach the tegmen. Upon the ventral disk there is a well 
defined anal ridge, which ends in a subcentral proboscidiform protuberance 
with the anus at the upper end. Interdistichals consisting of a rather large 
plate resting between the-sloping upper faces of the first distichals, and six 
or more rows of two plates each, the upper ones resembling the plates of the 
tegmen, Tegmen almost flat ; composed exclusively of small polygonal 
plates. In the casts there appear upon the surface ten well marked ridges, 
which represent grooves in the test for the reception of the ambulacra. 
florizon and Locahty. — Upper part of Niagara group; near Chicago, Ills. 
Ltemarks. — It probably occurs also at Waldron. Among the specimens 
which we refer to it there is one in which large portions of the arms are pre- 
served. They branch at about 18 mm. above the calyx, and one of the 
branches again at about 25 mm. above the first bifurcation. Whether 
any additional bifurcation takes place in this species, cannot be ascertained, 
as the arms are broken at 65 mm. from the calyx. The arms are composed 
of two rows of short, transverse pieces, very regularly arranged. 
Periechocrinus necis (Wincu. and Marcy). 
Plate L. Figs. La, 6. 
1865. Megistocrinus necis —WincuEt and Marcy; Mem. Bost. Soc. Nat. Hist., p. 110, Plate 2, Fig. 6. 
1881. Saecocrinus necis—S8. A. MituEr; Journ. Cincin. Soc. Nat. Hist., Vol. IV., p. 172, Plate 4, Figs. 
3, od. 
1885. Paice hocriins necis —W. and Sp.; Revision Paleocr., Part III., p. 106. 
A shorter species than the preceding. Calyx pyriform, not much higher 
than wide ; obconical to the top of the second radials; greatest width a little 
above the second costals, whence it contracts rapidly to the arm bases, at 
which the calyx is reduced to two thirds its former width. Surface of plates 
smooth, with slight angularities following the radials, giving to the cross- 
section a somewhat pentangular outline. 
Basals of medium size, more rapidly spreading than the parts above. 
Radials and costals occupying two thirds the height of the calyx, nearly of 
equal size, longer than wide; their upper and lower faces wider than usual 
in this genus. Distichals two; the first plate one third smaller than the 
costals ; the second as much as one half. Palmars two or more, small, and 
between them are interposed 1, 2, 2, small interdistichals. Interbrachials 
