ACTINOCRINID &. 597 
Physetocrinus ornatus , (Hatz). 
Plate LXIITL, Figs. 1, 2, 3, 4. 
1858. Actinocrinus ornatus —Hatt, Geol. Rep. Iowa, Vol. I., Part II., p. 583, Plate 10, Fig. 12. 
1873. Physetocrinus ornatus— Munx and Wortuen; Geol. Rep. Illinois, Vol. V., p. 849; also W. and 
Sp., 1881, Revision Paleocr., Part IT., p. 157. 
Syn. Actenocrinus senartus Haut; 1860, Suppl. Geol. Rep. Iowa, p. 25. 
Syn. Actinocrinus Britisi —8. A. Mitten; 1892, Adv. Sheets 18th Rep. Geol. Surv. Indiana, p. 36, 
Plate 6, Figs. 1-4. 
Calyx of medium size, depressed bowl-shaped to the top of the costals, 
thence spreading abruptly to the arm bases; the distichals and palmars Jon- 
gitudinally rounded and laterally inflected so as to form at the arm regions, 
between the rays and their subdivisions as well, deep grooves, which give to 
the calyx, as seen from above or below, a distinctly lobed outline. Ventral 
disk but very slightly convex. Plates exceedingly thin and delicate, beauti- 
fully ornamented with angular, well defined ridges, passing from plate to 
plate and meeting at their centres; those running up and down the radials 
and brachials the strongest, and dividing the surface of the dorsal cup into 
five nearly equal fields. 
Basals very small, represented by a short dentate rim, which slightly | 
projects beyond the column. Radials wider than long. First costals hex- 
agonal; the second equal to, or larger than the first. Distichals somewhat 
smaller, the interspaces deeply depressed and occupied by one or two small 
interdistichals; giving off an arm from one side, which is free from above 
its first plate, and a palmar from the other. The latter supports the second 
arm and a post-palmar, which in turn gives origin to two arms, there being 
four arms in each main division, and eight to each ray. Arms moderately 
thin; somewhat flattened in their upper portions. Pinnules composed of very 
long joints, bearing a small hook near the outer end. Regular interbrachials: 
1, 2, 2, 2; those of the second range almost as large as that of the first row, 
the two upper ones minute and on a level with the arm bases. Anal plate 
a little smaller than the radials, supporting 2, 3, 3, 2 plates. Interbrach- 
lals at all five sides in contact with the plates of the tegmen, as are also the 
interdistichals. Ventral disk deeply grooved near the arm bases, which 
gives to the surface a plicated aspect; it is composed of very small pieces, 
which are flat and quite irregular at the middle of the disk, but near the 
outer margins, where the small covering pieces of the ambulacra are exposed, 
