BATOCRINID 2. 535 
tact and alternate with one another. Anus at the end of a proboscidiform 
protuberance, within the arm regions or a little above or below. Column ~ 
large and long. In a large specimen it was found preserved to a length 
of three feet, but evidently was considerably longer; it gradually increased 
its diameter from 14 mm. at the top to 24 mm. at the distal end. Near the 
calyx, the nodal joints, which at their edges are rounded and somewhat un- 
dulating, project conspicuously over the youngest and those of intermediate 
growth, but farther down on the stem the latter attain the size of the oldest, 
and a wider joint always alternates with a narrower one. Toward the dis- 
tal end all the joints become of the same length and width, their proximal 
and distal surfaces are covered with fine radiating strize, and the lines of 
union are zigzag. Central canal extremely large, occupying one third the 
diameter of the joint, and obscurely pentalobate. The lower end of the 
column has not been observed, but from detached parts, which undoubtedly 
belong to this species, it appears that it was provided for quite a distance 
with long and stout branches, which were perforated by a canal of elon- 
gate form. 
Horizon and Locality. — Found in both divisions of the Burlington group 
up to the white crystalline layers of the upper bed; Burlington, Iowa, and 
Henderson Co., Ills. 
ftemarks.— The size of this species is extremely variable. Among the 
fifty-two specimens under examination, the calyx varies from 5 to 65 mm. 
in length, and from 7 to 85 mm. in width. Asa rule, the specimens from 
the Upper Burlington division are a shade larger, yet White’s type of 
Megistocrinus plenus, the Upper bed form, in the Museum of Comparative 
Zoblogy, is considerably smaller than the largest specimens from the Lower 
bed. MM. plenus was said to differ “by its convex base, prominent basal 
plates, channeled sutures, and the proportions of the body plates;” but 
neither one of these distinctions will stand when a large number of speci- 
mens are compared. The basals are not prominent in any of them — not 
even in the type —and the suture lines are not more channeled than they 
are in specimens from the Lower bed. Aectinocrinus minor, A. superlatus, and 
A, brevicornis, which we have always held to be one species, represent earlier 
stages in the development of Megistocrinus Evansi, as we suggested in the 
Revision (Part IL, p. 188). “ Actinoerinus”” minor with fewer anal plates, and 
the anal aperture much lower on the posterior side, represents the youngest 
form of the species, and A. superlatus and A. brevicornis a transition between 
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