308 SMITHSONIAN INSTITUTION 



Dactylocrinus excavatus (Schultze) 

 Plate XLI, figs. 5-6 



Zeacrinus excavatus Schultze, Mon. Echinodermen Eifler Kalkes, 1867, p. 39, text-fig. 6, pi. 7, figs. 2, 



2a, b. — Quenstedt, Petref. Deutschlands, IV, 1876, p. 514, pi. 108, fig. 25. 

 Zeacrinus excavatus var. interscapularis Schultze, Mon. Echinodermen Eifler Kalkes, 1876, p. 40, pi. 7, 



figs. 3, 3a, b. 

 Taxocrinus (Gnorimocrinus) excavatus, Wachsmuth and Springer, Revision Palaeocrinoidea, pt. I, 



1879, p. so. 

 Dactylocrinus excavatus, Jaekel, Zeitschr. d. deutsch. geol. Gesell., for 1897 [1898I, XLIX, p. 47. — 



Springer, Jour. Geology, XIV, 1906, p. 515. 



A rather small species. Crown relatively short and wide, with very broad 

 base. Height of calyx to width at axillary IIBr, i to 1.5 ; spread of calyx from 

 lowest point of curved radials, 1 to 1.4; cross-section decagonal, side outline 

 nearly straight and perpendicular. Base very broadly truncate, invaginated 

 into a very large deep cavity involving the whole of the basals except the pos- 

 terior, and a good part of the radials : it is so deep that the inf rabasals rest at 

 about the level of the lower IIBr. Surface smooth. Crown, 22 mm. high by 

 19 mm. wide; height of IIBn, 13 mm. ; base at outer edge of curvature, 13 mm. ; 

 inner diameter of basal concavity, 5 mm.; depth, 12 mm.; diameter of column 

 facet at bottom of concavity, 3 mm. 



IBB, BB, and lower part of RR all included within basal concavity and in- 

 visible in side view, except post. B which rises above distal face of RR; it is 

 succeeded by several anal plates in ranges of two or more abreast filling a tri- 

 angular area, above which the rays meet. iBr one elongate plate, or may be 

 entirely absent. Rays broad and short, inner ramus smaller than outer. Br 

 diminishing in width by steps from four times as wide as high at IBr to about 

 equal height and width at IIIBr 2 or 3. Intervals wide; first ramule on third to 

 fifth IIIBr, with similar intervals above; ramules small, not over one-third the 

 width of brachial, and probably not over three or four in number. Column not 

 preserved, but from space in basal cavity must have been of moderate size. 



The remarkable thing about this species is its extremely deep basal concavity, in which 

 respect there is nothing like it in any other species of the Flexibilia. That which in other 

 species of the genus is a more or less shallow concavity is here a complete invagination, 

 extending to the middle of the radials. It is so large, and rises to such a height in the middle 

 of the calyx, that the space for the viscera is greatly reduced, and must have been compen- 

 sated by a very high tegmen which is not indicated by the height of the crown as seen in the 

 fossil state ; it probably collapsed under contraction of the infolding arms. The curvature 

 for the invagination begins at about half way up the radials, which are recurved and form 

 the rim of the cavity ; the points of the regular basals do not appear at its edge, but they 

 extend inward and upward for a distance equal to the height of the radials and primibrachs 

 combined. In figure $c on Plate XLI the cavity is 12 mm. deep, measuring from the level of 

 the rim ; and allowing an average thickness for the plates the inner floor of the inf rabasals 

 would be at about the level of the top of the first IIBr, or nearly as high as the apex of the 

 triangular anal area. 



