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746 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Basal cup projecting laterally in form of a rim; its lower face slightly 
excavated for the reception of a large stem. MRadials about one third longer 
than wide, a little wider at the top than at the bottom; facets for the recep- 
tion of the costals about two-thirds the width of the plates; semicircular, 
and somewhat thickened at the lower margin; the limbs but slightly trun- 
cated. Costals two, forming a syzygy, the lines of union obscure; the 
hypozygal joints very short and subquadrangular, the epizygal, of which the 
lower part is placed within the facet, considerably longer and pentangular. 
Arms ten; stout, cylindrical, composed throughout of rather long, single 
joints, of which the upper and lower faces are parallel; the main trunks 
giving off armlets, one from each fifth or sixth joint, the intervening joints 
pinnule-bearing. The armlets extend to the same height as the main arms, 
but have only half their width. Both are composed of quadrangular joints, 
which are somewhat shorter than wide; while the pinnules are short, and 
their joints fully twice as long as wide. Armlets and pinnules are borne 
only on one side of the arms: in the anterior ray from the inner side, in the 
lateral rays from the outer one. There is but one interbrachial plate, but 
this was apparently followed by several rows of small, nodose, interambu- 
lacral pieces. Form and position of anus unknown. Column round; the 
nodal joints considerably widest, and distinctly rounded at their edges. 
Hlorizon and Locality. — Hamilton group, near Davenport, Iowa. 
Type in the Museum of the Davenport Academy of Natural Sciences. 
Remarks. — This species is peculiar for its arm structure, but still more 
for the arrangement of the pinnules. In the latter point it approaches 
Anomalocrinus caponiformis ; but while in that species. the position of the 
pinnules changes from one side to the other after each bifurcation, in this 
they are apparently given off from the same side throughout the full length 
of the arm. 
Hexacrinus Leai (Lvov). 
Plate LX XVIII, Figs. 12a, b. 
1869. Platycrinus Leai — Lyon; Trans. Amer. Phil. Soc. Phila., Vol. XIIL., p. 459, Plate 24, Figs, g. g/. 
1881. Hexacrinus Leai— W. and Sp.; Revision Paleocr., Part IL., p. 80. 
1889. Platycrinus Leai —S. A. Mittmr; N. Amer. Geol. and Paleont., p. 271. 
Of moderately large size. Dorsal side of the calyx semi-ovate; plates . 
thin and without ornamentation; the suture lines not grooved and rather 
obscure. 
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