44 
SMITHSONIAN INSTITUTION 
Cylicocrinus spinosus iie\y species 
Plate 7, figs. 30, 30a 
Founded upon an isolated hexagonal base with prominent spinose projecr 
tions, differing thus from all the other specimens. May be only a variant of 
the type. 
Horizon and locality, same as last. 
Subfamily PERIECHOCRININAE Bather 
BB 3. IBr hexagonal; iBr numerous, passing into iAmb; tegmen composed 
of numerous small undifferentiated plates. 
PERIECHOCRINUS Austin 
Plate 10 
Periechocrinitcs Austin-, Ann. Mag. Nat. Hist., lo, 1842, p. 109. 
Periechocrinus McCoy, Syn. British Foss., 1855, p. 56. — Wachsmuth and Springer, Rev. Pal., 2, p. 127 
(list of species) ; N. A. Crin. Cam., 1897, p. 519. — Bather, Treatise on Zool., 3, 1900, pp. 166, 168. — 
Zittel-Eastman, Textb. Pal., 2d ed., 1913, p. 194. — Jaekel, Phylogenie und System, 1918, p. 35. — 
Bassler, Bibliogr. Index, 1915, pp. 953, 954 (references, synonyms and list of American species). 
Calyx elongate, slender, expanding to the arm-bases ; cup-plates long and 
thin, with prominent axial folds along radial series ; rays bifurcate two or three 
times within the cup, leading to from 20 to 40 free arms, biserial, and usually 
not branching after becoming- free. 
Genotype. Actmocrinites moniliformis Phillips. 
Distribution. Silurian ; Gotland, England, America. 
Of the large number of Silurian species which have been referred to this genus, at least 
one is from England, 9 are from Gotland, and ii from North America. The latter are dis- 
tributed as follows : Rochester shale, i ; Laurel limestone, 2 ; Waldron shale, i ; Brownsport, 3 ; 
Racine dolomite, 4. Besides these are two from the Lower Carboniferous, and one in Europe 
from the Devonian which may go better under Saccocrinns. 
The typical form, as represented by the abundant and well known English species, 
P. moniliforniis, is well marked and readily distinguished by the extremely elongate, slender 
cup, thin plates, unusually high RR and IBr with their conspicuous axial folds running to the 
arm-bases. Several species of that type have also been described from America, but along 
with them are some others which while having the same general calyx arrangement are want- 
ing in the above characters, having the cup-plates lower, thicker, more convex and without 
folds. Taking as an example of this type such a form as the Carboniferous P. whitei, pictured 
in N. A. Crin. Cam., pi. 6, fig. i. one is impressed with the force of the doubt with which it 
is listed. In the Zittel-Eastman Textbook, edition of 1913, I undertook to revive Hall’s dis- 
carded genus Saccocrinns as a receptacle for some of these non-characteristic species, and 
am making the distinction accordingly here for two species. An entirely new form for the 
Tennessee Silurian turned up in the Beech River formation, clearly belonging to the English 
and Swedish type, but unfortunately too much injured for a specific definition. 
