LARVIFORM CRIXOIDS 35 



Occurrence. — -The holotype, which is entirely silicified, was obtained 

 from a dark limestone near the base of the Pennsylvanian strata near the 

 center of the N. y 2 sec. 35, T. 21 N., R. 9 W., Warren County, Indiana. 



Genus TYTTHOCRINUS 9 J. M. Weller, n. gen. 



Genotype Tytthocrinus comptus J. M. Weller, n. sp. 



Tytthocrinits differs from Amphipsalidocrinus in the further degenera- 

 tion of its radials and arms. This form is armless and the radials are either 

 exceedingly minute or absent. The anal opening has been displaced farther 

 to the right and lies nearly in the right posterior radius. 



Tytthocrinus comptus J. M. Weller, n. sp. 



Plate II, figs. 7a-b 



Description. — The calyx is very small and somewhat broader than high. 



The height of the holotype is .44 mm. The body expands rapidly from a 



moderately sized stem facet to the gently sloping 



subpentagonal distal surface. The arrangement and 



number of the plates is not certainly known because 



of the indistinct sutures separating them, but they 



Fig. 7 appear to be disposed in three circles, ( 1 ) a very low 



interpretation of the calyx infrabasal disc, (2) a ring of low basals, and (3) five 



structure of Tytthocrinus , i i • 1 • 1 ^i i i. r ^i i 1 



comvtus (compare with large orals which inclose the greater part ot the bodv 



PI. II, fig. 7a). 



cavity. 

 The infrabasal disc is very low and forms about one-eleventh of the 

 total height of the calyx. Its lower surface is the circular stem facet having 

 a diameter equal to about two-fifths of the maximum width of the body. 

 It is flat and pierced by a single central opening. The sides of the infra- 

 basal disc rise nearly vertically and the position of its upper margin is marked 

 by a very slight constriction which passes around the crinoid just above its 

 base beyond which small obtuse points project into the angles between the 

 basals. 



The basals are low and form about three-elevenths of the total height of 

 the calyx. The sutures separating them can not be made out but the basals 

 are apparently subpentagonal in outline and somewhat wider than high. It 

 is possible that some of them are larger than others. No indication of radials 

 has been observed. 



The comparatively large anal opening is situated between the ring of 

 basals and the orals. Although it occurs in the posterior interradius it is 

 strongly displaced to the right, nearly to the right posterior radius. 



8 tvtBos, small. 



