THYSANOCRINID&. 211 
Distribution. — Only known from the Niagara group of America. 
Type of the genus. — Siphonocrinus armosus (McChesney). 
Remarks. — This genus, by its asymmetrical form, is closely allied to 
Lampterocrinus, from which it differs as stated under that genus. 
S. A. Miller, in proposing the genus, described it as having three infra- 
basals. We have examined more than eighty specimens, from the collections 
of Mr. W. C. Egan of Chicago, and Mr. F. A. Greene of Milwaukee, and 
satisfied ourselves that they all have five plates in the proximal ring. 
In studying the figures, it must not be overlooked that most of them 
represent natural casts of the iuternal surface of the test, the plates them- 
selves having been dissolved by chemical action, and that on these all eleva- 
tions represent depressions of the inner floor. Only in the figures made 
from casts in the natural moulds does the surface represent the true external 
surface of the plates. 
Siphonocrinus armosus (McCuesyey). 
Plate XIX. Figs. 8a, b, c. 
1859. Eucalyptocrinus armosus —McCuxsney; Descr. New Paleoz. Foss., p. 95. 
1867. (?) Glyptocrinus armosus — McCursney; Trans. Acad. Sci. Chicago, p. 23, Vol. I., Plate 7, Figs. 
6a, 6. 
1881 (?) Glyptaster armosus —W. and Sv.; Revision Paleocr., Part IL, p. 196. 
1882. Glyptocrinus armosus — WHITFIELD; Geol. Surv. Wis., Vol. IV., p. 284, Plate 16, Fig. 11. 
1888. Siphonocrinus armosus —S. A. Mixter; Amer. Geologist, Vol. I., p. 264. 
Syn. Glyptocrinus siphonatus — Hau; Rep. of Progr., Geol. Surv. Wis., p. 22; and 20th Rep. 
N. York State Cab. Nat. Hist., Plate 10, Fig. 11. 
A large species, only known from internal casts. Calyx subovoid. Dorsal 
cup generally higher than the ventral disk, its sides decidedly convex, sub- 
globose ; section across the arm bases slightly lobed. 
Infrabasals small, forming a shallow cup. Basals as large as the first 
costals, the upper angles unusually sharp, exceptionally touching the inter- 
brachials. Radials larger than the costals; the first costals larger than the 
second, and hexagonal. Distichals and palmars in series of two each. Arms 
four to the ray, their structure unknown. The plates of the regular inter- 
brachial spaces generally consist of four rows, arranged: 1, 2, 2, 3; the first 
plate as large as the first costal. Anal interradius considerably wider, greatly 
bulging from below the arm bases; the first anal higher than the radials, 
succeeded by three plates in the second and third rows, and numerous irre- 
gular, rather large plates at the disk. The latter plates together form 
a trumpet-shaped inflation, apparently representing a subtegminal anal tube, 
