PISOCRINIDAE 
83 
mens showing the structure of the tegiiien and marginal brachials clearly are 
rare. The foregoing description is made from twelve specimens in which the 
groups of three brachials and the interposed orals are distinctly shown. In 
these small specimens the sutures in the tegmen are usually rather obscure. 
Mr. Chapman’s enlarged figure 22 on plate 25 was made many years ago after 
a careful study of two well preserved specimens. A specimen subsequently ac- 
quired, figures 21, 2ia, having the oral plates slightly parted, confirms the 
original figure in every particular. The species ranges in size from 5 to 10 mm. 
height to the top of the radials ; the latter figure is rare, the usual height being 
from 6 to 8 mm. 
Horizon and locality. Laurel limestone ; St. Paul and Greensboro, Indiana ; and Beech 
River formation; Flatwoods, Perry County, Tennessee; perhaps Racine dolomite; Lemont, 
Illinois. 
Zophocrinns glohosus Slocom, Field Columb. Mus., Geol. Ser. 2, 1908, p. 285, pi. 85, 
figs. 15-19, from near Lemont, Illinois, and Zophocrinns pyriformis Slocom, ibid., page 285, 
plate 85, figures 12-14, from Romeo, Illinois, are both referred to the Racine division of the 
Niagaran. 
MYSTICOCRINUS Sp ringer 
Plate 26 
springer, Amer. Jour. Sci., 46, 1918, p. 666. 
Calyx globose, rigid, with no indication of loose suture or flexibility; lower 
brachials do not take part in calyx wall. Dicyclic; IBB 3, the small plate in 
r. post, position. RA in primitive position below r. post. R. being the lower 
segment of that radial, which (and no other) is compound. RR unequal, with 
lateral processes projecting between arm-bases; facets curved and excavated, 
not filling distal face of radials. Anal plate i, large, angular above, projecting 
above level of radials ; opening unknown. Arms uniserial, branching once, com- 
posed of only a few brachials. Tegmen narrow, probably covered by a pyramid 
of orals as in Pisocrinits and S ymbathocriniis . 
Genotype. Mysticocrinus wilsoni Springer. 
Distribution. Silurian ; not known outside of America. 
This diminutive crinoid, described by me in 1918 from a very perfect specimen, and of 
which a fragment of another slightly larger is known, is of a wholly novel type, with such a 
complex assemblage of characters that its systematic position is uncertain. It is an Inadunate, 
superficially resembling the Larviformia, and upon a preponderance of characters coming 
nearer to that group than to any other. The primitive radianal is against it, and the dicyclic 
base also, although the latter may fall within an admitted exception. It would seem to be 
intermediate between the Larviformia and the Fistulata ; in the primary composition of the 
cup, especially in the radianal under the right posterior radial, it is similar to the Dendro- 
crinidae, although wholly unhke them in the dwarfed arms and interbrachial processes, both 
of which are Larviformia characteristics. The 3 IBB, with small plate at right posterior, is a 
character of the Flexibilia, from which it is excluded on other grounds. 
