Tr 
ACTINOCRINID&. 637 
there is nothing between the two forms that could not be readily explained 
_ by individual growth, except the great contrast in the size of the specimens, 
which on the one hand are quite large, and on the other very small, the 
intermediate forms being wanting. This in part has led us to propose a new 
name for the larger form; but the principal reason is that it is practically 
impossible to recognize the species, or even the genus, from Meek and 
Worthen’s description. 
STROTOCRINUS M. and W. 
1866. Mzzx and Wortuen (including Zeleiocrinus) ; Geol. Rep. Illinois, Vol. I1., p. 188, and Proe. Acad. 
Nat. Sci. Phila., p. 2538. 
1878. Zrvret (including Teleiocrinus and Physetocrinus); Handb. d. Paleont., Vol. I., p. 370. 
1881. W. and Sp.; Revision Paleocr., Part II., p. 158 (Proceed. Acad. Nat. Sci.-Phila., p. 332). 
1889. §S. A. Minter; North Amer. Geol. and Paleont. p. 283. 
Syn. Calathocrinus Wat (Subgenus of dActinocrinus), 1861; (not von Meyer 1848, Bronn’s Jahr- 
buch, p. 469). 
Strotocrinus holds the same relation toward Physetocrinus that Teleio- 
crinus does toward Cactocrinus ; the first two being distinguished by having 
an anal opening within the disk, while the last two have an anal tube. In 
the construction of the calyx as far as the top of the distichals, all these 
forms differ only immaterially ; but from the palmars up in Strotocrinus, as 
in Telewcrinus, owing to the great increase in the number of arms, the 
brachials were crowded outwards and formed a broad, continuous, ten-rayed 
rim, in which not only the lower parts of the arms, but also the lower pin- 
nules, became incorporated. The specimens are of very large size, and the 
number of arms enormous, the disk sometimes attaining a width of 12 cm., 
with as many as fifteen bifurcations in each division, or one hundred and fifty 
arms altogether. The arms are given off alternately from opposite sides, 
each order consisting of a single axillary plate, which supports at one side an 
arm, a brachial of a higher order at the other, and the uppermost one two 
arms. The arms are thin and comparatively short. Interbrachials not 
numerous, and never extending beyond the palmars. Disk flat or very 
slightly convex ; composed of thousands of minute, irregular plates, which 
decrease in size as they approach the arms. Anal opening excentric, rarely 
rising above the general plane of the disk. 
Distribution. —Restricted, so far as known, to the Upper Burlington lime- 
stone of the Mississippi Valley. 
Type of the genus: Strotocrinus regalis. 
