746 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



Basal cup projecting laterally in form of a rim ; its lower face slightly 

 excavated for the reception of a large stem. Eadials 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 thicl^ened 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 ai'e 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. 



Horizon 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 caponifonnis ; but while in that species the position of the 

 pinnules changes from one side to the otiier after each bifurcation, in this 

 they are apparently given off from the same side throughout the full length 

 of the arm. 



Hexacrinus Leai (Ltox). 



Plate LXXVIII. Figs. ISa, h. 



1S69. Plati/crinm Tmi — 'Lro^; Traus. Anier. Pbil. Soc. Phila., Vol. XUL, p. 459, Plate 24, Y\gs,g.gl. 

 1881. Hexacrinus Leai — W. and Sp. ; Revision Palffiocr., Part II., p. 80. 

 1889. Flatycrinus Leai — S. A. Millek; N. Amer. Geol. and Palseont., 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. 



