ACTINOCEINID^. 597 



Physetocrinus ornatus (Hall). 

 Plate LXIII. Figs. 1, 2, 3, 4- 



1858. Actimcrinns ornatus — Hall, Geol. Rep. Iowa, Vol. I., Part II., p. 5S3, Plate 10, Fig. 12. 

 1873. PhysetocTums orimins — Meek and Wobthen; Geol. Eep. Ulinois, Vol. V., p. 349; also "W. and 

 Sp., 1881, Revision Palfeocr., Part II., p. 157. 

 Syn. Actinocrbms senarius Hall; 1860, Suppl. Geol. Rep. Iowa, p. 25. 



SjE. Actinocrinus Brittsi — S. A. MiLLEE; 1892, Adv. Sheets 18tli Eep. Geol. Suit. 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 disticlials and palmars lon- 

 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 

 fi.ve nearly equal fields. 



Basals very small, represented by a short dentate rim, which slightly 

 projects beyond the column. Eadials 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. Eegular 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- 

 ials at all five sides in contact with the plates of the tegmen, as are also the 

 interdistichals. Ventral disk deejDly 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, 



