72 
SMITHSONIAN INSTITUTION 
PISOCRINUS De Koninck 
Plates 2^, 24, 25 
Pisocrinus De Koninck, Bull. Acad. Roy. Belgique, 2me. ser., 4, 1858, p. 93. — Angelin, Icon. Crin. Suecc., 
1878, p. 20. — Wachsmuth and Springer, Rev. Pal., 3, 1886, p. 172. — S. A. Miller, Jour. Cin. Soc. 
Nat. Hist, 1879, p. 10; Am. Geol., 1890, p. 356; 17th Ann. Rep. Dep. Geol., Indiana, 1892, p. 636- 
642 (adv. sheets, pp. 26-32). — Bather, Crin. Goth, 1893, p. 21; Treatise on Zooh, 3, 1900, p. 149, 
fig. 62. — Jaekel, Zeitschr. d. D. Geol. Gesell, 1900, p. 482; Phylogenie und System, 1918, p. 89. — 
Etheridge, Rec. Australian Mus., 1904, p. 289. — Zittel-Eastman, Textb. Pah, 1913, p. 208. — Thomas, 
Proc. Iowa Acad. Sci., 22, 1916, p. 291. — Bassler, Bibliogr. Index, 1915, p. 980. 
Triacrimis Ringueberg (not Munster), Proc. Acad. Nat. Sci. Phil., 1884, p. 144. 
Crinoids of very small size. BB 5, unequal; r. p. and r. a. truncate distally 
and smaller than the other three, which are angular above. RR unequal and 
unsymmetric; 1 . post, and ant. large, widest below, and meeting BB by trun- 
cate faces, the other three RR small, angular below and not touching BB; 
r. post. R. transversely bisected, the large lower segment serving as inferradial 
for it and the r. ant. R. thus forming- the RA, which separates them both from 
BB ; this plate and the two large RR constitute the greater part of the calyx. 
Arms 5, unbranchcd non-pinnulate, composed of very long brachials beyond 
the first, which is short; they spring from indented facets at the middle of the 
radials bounded by processes or partitions at either side projecting upward and 
inward; the processes are various in form and size, from low, narrow, rectan- 
gular, to high, wide and of spear-head shape, that on the posterior side, formed 
by the right and left posterior radials, being lower and wider than the others, 
and curved inward for support of the anal tube. Tube crescentic or triangular 
in section, resembling an arm. Tegmen arched by 5 solid orals which interlock 
at the center, meet closely at their lateral faces, and connect with the radial 
processes. Stem round, with short columnals, thickened in the middle. Surface 
usually smooth, exceptionally tubercular. (See generic diagram, pi. 23, fig. 46.) 
Genotype. Pisocrinus pilula De Koninck. 
Distribution. Silurian ; Gotland, England, America, Australia. 
Pisocrinus is a form of cosmopolitan distribution, being found almost wherever Silurian 
strata are exposed, not only in Europe and America, but also in the antipodes, two species 
having been described from Australia. A characteristic fossil of the Wenlockian beds of 
England and Sweden, from the former of which it was first described, the genus has been 
recognized from American rocks in New York, Ohio, Indiana, Illinois, Iowa, Missouri and 
Tennessee, in almost all the subdivisions of the Silurian from the Clinton and Osgood to the 
Racine dolomite and the Eouisville. In some of these areas it is an important guide fossil. 
Species are numerous, and in some of them individuals are abundant. Comparison of Euro- 
pean and American species shows a striking correspondence in some of them, which con- 
trilnites important evidence of a migrational connection by way of a northern route between 
the faunas of northern Europe and the United States during Silurian epochs. 
For a full discussion of the i-elations of Pisocrinus and the literature concerning it, 
reference should be had to Dr. Bather’s Crinoidea of Gotland, 1893. The parallelism of 
European and American species is recognized, being emphasized by the statement on page 27 
