CRINOIDEA. 67 



Base hexagonal, convex, basals ankylosed; size of column facet unknown; axial 

 canal quinquelobate, 1/3 diameter of base. 



All plates of the radial cycle hexagonal, almost perpendicular; radials slightly 

 larger than anal x. Primibrachs 2x5, IBri smaller than IAx. Arrangement of brachials 

 above IAx as given in the generic description. Primary interbrachials arranged 1, 2, 2, 

 or 3, 2; ill Br in the bivium 1, in the trivium 2; anal interray X, 3, 2, 2. ill I Br 1 or more. 

 All interbrachials meeting interambulacrals. 



Tegmen slightly elevated centrally, flattered marginally; plates convex, numerous, 

 of irregular form and size, sutures indistinct. Anal tube about 1/7 diameter of tegmen, 

 excentric, about 1/3 the diameter in from the back margin. 



Column and arms unknown. 



Remarks — The species as represented by a single specimen is characterized by 

 great width, low dome, shallow cup, and deep aboral depression. The type is somewhat 

 misshapen on account of crushing and the cup may have been slightly deeper than 

 shown in the figure. 



Megistocrinus missouriensis differs from all species herein cited in the great width 

 at the arm bases and flatness of its tegmen. 



Occurrence— M'meola limestone, 4 miles south of Montgomery City. 



Order Flexibilia 



Family Ichthyocrinidae 



Genus Dactylocrinus Quenst. 



Dactylocrinus concavus (Rowley) 

 Plate 7, figures 4 and 5 



1893. Taxocrinus concavus Rowley, Am. Geologist, XII, pp. 304-305, pi. 14, fig. 2. 



1894. Taxocrinus concavus Rowley, Am. Geologist, XIII, pp. 153-154, figs. 3 and 9. 



1895. Aristocrinus concavus Rowley, Am. Geologist, XVI, pp. 217-219, figs 1 and 2. 

 1902. Aristocrinus concavus Keyes, Bull. Geol. Soc. America XIII, p. 285. 

 1909. Aristocrinus concavus Greger, Am. Jour, Sci., XXVII, p. 376. 



1920. Dactylocrinus concavus Springer, The Crinoidea Flexibilia, Smithsonian Institu- 

 tion, pp. 309-310 plate 41, figs. 7a, b, c, 8a, b, c, 9. 



Springer's description — "A rather small species. Crown short, rotund, with broad 

 base; contracting above the inter-axial, where height to width is 1 to 2.2 ; spread of calyx 

 from outside of basal rim, 1 to 2; cross-section obtusely pentagonal, side outline curved. 

 Base broadly and shallowly concave, resting on basals and lower incurved points of 

 radials. Surface smooth. Crown of mature specimen, 25 mm. high by 22 mm. wide; 

 base at line of curavture of rim, 11 mm., column facet, 5 mm. 



Infrabasals small, wholly covered by the column. Basals curving from basal cavity 

 to outside of rim; their points visible in side view; post-basal truncxte, not rising to 

 top of radials, followed by small anal, and this by two series of 3 or 4 plates tapering 

 to an apex between posterior rays. Interbrachials one very large plate, rising to top of 

 distichals, with a wide, rounded, distal face, probably for attachment of perisome. 

 Interdistichals present in large specimens. Radials unusually large for the genus — 

 the largest plates in the calyx. Costals much shorter and narrower. Rays and their 

 divisions deeply rounded, tapering but little; the inner branch the smaller; distichals 

 usually 3, occasionally 2 or 4. Ramules small, 4 to 6 visible below point of infolding; 

 intervals usually of 3 or 4 brachials, shorter in the distal portions. Column small, with 

 thin ossicles next to calyx. 



A well-marked and constant species, nearer to D. excavatus than to any other, 

 but without its deep basal cavity; otherwise distinguished by its longer, more rounded, 

 and less tapering ray divisions. In that species the ramules become equal to the main 



