NO. 6 NEW AMERICAN EDRIOASTEROIDEA BASSLER 21 



DISCOCYSTIS Gregory, 1897 



This genus, of which three well-marked species are now known, 

 exhibits the essential characters of Agelacrinites except that four of 

 the ambulacra are curved to the left and one, the right posterior, to 

 the right, and the theca is more sacklike, with many rows of closely 

 imbricated marginal plates. The genotype, Echinodiscus optatus 

 Worthen and Miller (pi. i, fig. 5), was based upon the basal side 

 of a specimen oi D. (Agelacrinus) kaskaskiensis. Besides the geno- 

 type and the following new species, the genus includes D. (Echino- 

 discus) sampsoni (Miller), 1891, from the Warsaw of Missouri. 



DISCOCYSTIS LAUDONI, n. sp. 

 Plate 3, figs. 7, 8 



This fine species, the types of which were collected and presented 

 by Dr. L. R. Laudon, of Tulsa University, is readily distinguished 

 by its narrow, well-developed long ambulacra curving decidedly 

 throughout their length. In D. sampsoni and D. kaskaskiensis the 

 ambulacra are comparatively straight for the first third of their length 

 and then curve rather abruptly. In other features these three species 

 show the generic characters very uniformly. 



Occurrence. — Kinderhook (Gilmore City formation), Gilmore 

 City, Iowa. 



Cotypes.— U.S.N. M. no. S- 



DISCOCYSTIS (AGELACRINUS) KASKASKIENSIS (Hall), 1858 



Plate I, figs. 4, 5 ; plate 3, figs. 4-6; plate 7, fig. il 



Agelacrinus kaskaskiensis Hall, Geol. Iowa, vol. i, pt. 2, p. 696, pi. 25, fig. 18, 



1858. 

 Echinodiscus optattis Worthen and Miller, Geol. Surv. Illinois, vol. 7, p. 336, 



pi. 18, fig. 3, 1883. 



The original type of this species failed to show clearly the direction 

 of curvature of the fifth arm, so Hall's illustration is here corrected 

 (pi. I, fig. 4). The great width of the zone of marginal plates (pi. i, 

 fig. 5, pi. 7, fig. 11) restricts the attached part of the theca to a small 

 circular central opening. Specimens with an abnormal number of 

 arms occur here as in other edrioasteroids, as shown on plate 3, 

 figure 5. The covering floor plates of the ambulacra are in distinct 

 uniserial rows (pi. 3, fig. 6). 



