562 THE CEINOIDEA CAMEEATA OF NORTH AMEEICA. 



lacral plates large and spinous, the interambulacral plates small and flat. 

 Anal tube central and apparently large ; its length unknown. 



Horizon and Locality. — Keokuk group; Keokuk, Iowa, and Nauvoo, 

 Hamilton, and Warsaw, Ills. 



Type in the (Worth en) Illinois State collection, Springfield. 



Actinocrinus Lowei Hall. 

 Plate LIV. Fig. 2. 



1858. Hall; Geol. Rep. Iowa, Vol. I., Part H., p. 611, Plate 15, Pigs. 5a, b. 

 1881. W. and Sp. ; Revision Palseocr., Part II., p. 144. 



Sya. AcHiiocriims broiites Hail; I860, Suppl. Geol. Rep. Iowa, p. 47. 



A large species, generally foimd in a flattened or crushed condition, 

 ■which makes it difficult to ascertain the actual form of the calj'x, though 

 it seems to be near that of A. pernodo&us ; but the brachial extensions are 

 larger, their plates proportionally longer, the interbrachial depressions 

 deeper, and the tegmen higher. Besides, it has eight arms to the ray 

 in place of six. The ornamentation is nearly the same as in that species, 

 but somewhat more symmetrical ; the plates are thinner, and the central 

 nodes less prominent. 



Basals large, forming a slightly spreading cup, a little thickened at the 

 sides, rounded on the lower margins, and the place for the attachment of the 

 column slightly excavated. Radials large, as long as wide, or longer. First 

 costals generally hexagonal, less than half the size of the radials. The 

 second costals smaller than the first, directed obliquely outward, and in- 

 curving at the sides to form the bases of the brachial extensions, which 

 from the distichals extend horizontally to the bases of the free arms, widen- 

 ing outwards. The brachials of the higher orders are comparatively large, 

 slightly nodose on the back, the sides incurving and deeply grooved, espe- 

 cially between the main divisions, where the grooves are also wider, and have 

 at the bottom a longitudinal row of three or four interdistichals. Distichals 

 wider than the costals ; all axillary, giving off at their outer sides an arm, 

 which is free from the third plate, at the inner two palmars, which from the 

 axillary support the second arm and two post-palmars, of which the upper 

 one bifurcates again, and sustains two arms. The arms themselves have not 

 been observed. Regular interbrachials : 1, 2, 3, 8 ; the outer ones of the 



