RHODOCRINID.E. 219 
brachials, the second row consisting either of two or three pieces. When 
there are two plates at the regular sides, the anal side has always three, but 
when the former has three, there is no additional plate at the anal side. 
Ventral disk narrow, rising but little above the dorsal cup; composed of 
irregularly arranged plates, none of which can be recognized as orals. Disk 
ambulacra subtegminal. Anus excentric, sometimes marginal. Column 
round; the axial canal pentagonal or stelliform; the internodes frequently 
consisting of but one joint. 
Distribution. — Rhodocrinus first appears in America in the Hamilton 
group; it attains its climax in the Kinderhook and Burlington beds, and 
becomes extinct at the end of the Keokuk epoch. Specimens, as a rule, are 
rare. In Europe the genus occurs in the Fheinisch Uebergangsgebirge, and it 
is represented by several species in the Mountain limestone. 
Type of the genus: Rhodocrinus verus Miller, from the Carboniferous of 
England. 
Remarks. — Rhodocrinus verus, according to J. 8. Miller, occurs in the 
Mountain limestone of Yorkshire, and also in the Wenlock limestone of 
Dudley, England, and it was said to have three basal plates. Miller con- 
founded two very different types, which have since been recognized as 
distinct genera. The Carboniferous form, which took Miller’s specific name, 
is universally regarded as the type of the genus Rhodocrinus, having five 
infrabasals instead of three, and biserial arms; the Silurian form from Dud- 
ley, with three infrabasals and single arm joints, was described by Phillips as 
Sagenocrinus expansus. 
The genus Phodocrinus, as we understand it, includes species with smooth, 
nodose, and spiniferous plates. For a certain species with spinous plates 
from the Devonian, Roemer proposed the genus Acanthocrinus. We have 
carefully examined the figures of A. longispinus, as given by Wirtgen and 
Zeiler,* but have failed to discover any characters by which this form can 
be separated even subgenerically. Spinous projections on the basals and 
radials occur quite frequently also among Carboniferous species in all possible 
variations. It is possible that ‘“ Rhodocrinus gonatodes” Miiller belongs to 
Oehlert’s new genus Diamenocrinus. 
We have referred Rhodocrinus microbasilis and R. pyriformis, both of 
Billings, to Archeocrinus ; R. vesperalis White to Diabolocrinus ; R. melissa 
Hall to Lyricerinus ; R. Halli Lyon to Thysanocrinus ; R. stellaris de Koninck 
* Verh. d. Naturhist. Verein, Jahrg. XII., Tab. II. 
