INVERTEBRATES. 183 



Poteriocrinus Swallovi, M. and W. 



PI. 16, Figs. 4a, 46. 



Poteriocrinus Swallovi, Meek and Worthen, Sept. 1860. Proceed. Acad. Nat. Sci. 

 Philad., p. 394. 



Body below the arms abconical, or tapering regularly down 

 to its connection with the column ; composed of smooth, nearly 

 flat plates, connected by linear sutures. Base small, basin- 

 shaped, truncate below, and widening gradually upwards, about 

 half as high as wide, and composed of nearly equal pentagonal 

 pieces; columnar facet comparatively large, a little concave, 

 without a marginal rim, and pierced by a pentapetalous cen- 

 tral opening, apparently less than one third the diameter 

 of the column. Subradial plates unequal, some of them as 

 long as wide, and others wider than long, three hexagonal, and 

 two on the anal side, which are larger than the others, hepta- 

 gonal. First radial plates smaller than the subradial pieces; 

 all wider than high, pentagonal, and truncated above, the upper 

 side being longer than either of the others. Second radials 

 very short, about twice as wide as high, some of them some- 

 what wedge-shaped, or a little longer on one side than the 

 other. Third radials short, or about twice as wide as high, 

 four of them pentagonal and supporting the principal divisions 

 of the arms on their superior sloping sides. In the anterior ray 

 the third radial plate, instead of being a bifurcating piece, is 

 truncated a little obliquely above, and succeeded by thirteen 

 other radials; all of which, excepting the last, are very short, 

 and alternately a little wedge-shaped; while the last one is 

 larger than the others, pentagonal in form, and supports two 

 divisions of the arms, similar to those in the other rays above 

 the second bifurcation. 



The first anal piece is pentagonal and rests between the 

 upper sloping edges of two of the subradials, while its right 

 superior sloping side supports one of the under sides of a first 



