‘“ACTINOCRINID ZA. 629 
over the sides of the two or three proximal stem joints; the suture lines 
deeply notched, the grooves reaching to the top of the plates. Radials as 
long as wide, and as large as both costals together; the second costals 
smaller than the first. Distichals as large as the axillary costals; the suc- 
ceeding brachials much smaller, giving off the arms in the usual way. Large 
specimens have seven bifurcations in each main division, and hence sixteen 
arms*to the ray, smaller ones five to six, with twelve to fourteen arms. 
Arms of moderate length and quite delicate, their lateral margins serrated. 
Regular interbrachials: 1, 2, 2, 2, gradually decreasing in size upwards. 
Anal plate generally a little smaller than the radials, followed by 2, 4, 3 and 
2 plates. Ventral disk almost flat at the margin, dome-shaped above. It 
is composed of large and small plates, the former nodose, the latter convex 
and interposed between the larger ones. Anal tube central, stout and long, 
rising above the tips of the arms, and constructed of rather small, convex, 
transversely elongate pieces. Column of less than medium size; the nodal 
joints long, their outer margins crenulated, being covered with numerous 
small, longitudinal processes, which hang down slightly over the intervening 
smaller joimts. 
Horizon and Locality.— Upper Burlington limestone, Burlington, Iowa, 
Quincy, II]., and other places. 
Type in the (Worthen) Illinois State collection. 
Remarks. —We have examined of this species over one hundred speci- 
mens of all sizes, most of them calyces, but some with the arms attached, 
and find among them considerable variation in the ornamentation (compare 
Plate LX. Fig. 2a with 26), as well as in the number of arm openings, 
without showing any other structural differences ; they even agree in the 
peculiar and unique ornamentation of the stem. A careful comparison of 
these specimens has shown us no way by which a separation of them can be 
made upon any constant characters. We have observed that the younger 
specimens have fewer arms than the older ones, and that the number of arm 
openings increased as the rim grew larger, 7. e., extended out farther. We 
also found that the specimens in their earlier phases passed through the 
Cuctocrinus stage, where they had no rim, and in which some of the higher 
bifurcations took place in the free arms (Plate LX., Fig. 2d), Among the 
calyces, the smallest ones have but 4 arm openings to the ray, somewhat 
larger ones 6, others 8, 10, 12, or 14, while in the largest ones there are 16; 
showing again how little reliance, in some groups, can be placed upon the 
