RHODOCRINID^. 241 



pieces, alternately arranged. They separate at the eighth or tenth plate, 

 when they bend abruptly outward in opposite directions, and each simple 

 tube is thence composed of three rows of pieces. Arms short, pendent, and 

 recumbent; they are composed of two rows of plates, and pinnulated. 

 There being six arms to each arm opening, three to each main division, 

 but rarely more than three are exposed to view, the others being covered by 

 the appendages. 



Horizon and Locality. — Keokuk group; Indian Creek, Montgomery Co., 

 Ind., where it has been found in splendid preservation. 



Types in the collection of Wachsmuth and Springer. 



GilbertSOCrinnS ObOVatUS Meek and Worthed. 

 Plate XVII . Figs, 4a, h. 



1869. Goniasferoidocrimis obovatus—MY,^.^ and Wouthen ; Proceed. Acad. Nat. Sci. Phila., p. 76 ; and 



1873, Geol. Rep. Illinois, Vol. V., p. 391, Plate 4, Pig. 6. 

 1881. OUacrinus obovafus — W. and Sp. ; Revision Palseocr., Pt. II., p. 219. 



Calyx urn-shaped; basal concavity deep, but narrower than in any of the 

 other species ; the sides of the dorsal cup convex, constricted at the arm 

 bases ; greatest width across the second costals ; ventral disk perfectly flat. 

 Plates without ornamentation, strongly convex, and of rather uniform size. 



Infrabasals small, forming together with the lower part of the basals 

 an inverted cup. Basals larger than any other plates of the calyx, bending 

 abruptly upwards and exposing two thirds of their surfaces in a side view. 

 Radials a little longer than wide, slightly larger than the costals, the lower 

 faces distinctly angular ; the interradial plates considerably smaller. Dis- 

 tichals two, larger than the adjoining interbrachials ; the second smaller 

 than the first. Arm openings proportionally small, at the bottom of a 

 shallow pit. Calycine appendages confluent at the proximal end, and 

 interradially disposed. Each pair, before separation takes place, is composed 

 of six rows of plates, and each tube pierced by a moderately large central 

 canal. Length of appendages unknown, as is also the form and construction 

 of the arms. Interradial areas elliptical, arched by the distichals and the 

 plates supporting the appendages ; they are composed of about thirteen 

 plates ; arranged : 1, 3, 3, 3, 3, or 1, 3, 3, 2, 2, with slight variations at the 

 anal side. Interdistichals six to eight, the first touching the axillary distichal. 

 Plates of the ventral disk rather large and strongly convex ; the interradial 

 depressions small, embracing only one or two pieces. Orals not distinct from 



31 



