File:The Quarterly journal of the Geological Society of London (13859873553).jpg

298
P. H. CAKPENTEE ON THE EELATIONS OF
31. On the Relations of Hyboceines, Baeeoceinus, and Hybo-
cystites. By P. Heebeet Caepentee, Esq., M.A., Assistant
Master at Eton College. Communicated by Prof. P. Maetin
Dencan, 1T.B. Lond., F.R.S., Y.P.G.S. (Read May 10, 1882.)
.Plate XI..
The Crinoids from the Lower Silurian of Canada for which the
genus Hybocrinus was established by Billings* in 1856 are remark-
able for the protuberance of the anal side of the cup, so that it has
somewhat of a humpbacked appearance, as is expressed in Billings's
generic name. Resting on the stem are five pentagonal basals,
above and alternating with which is a row of five plates (fig. I. a,
and PI. XI. figs. 3, 4, 5). Four of these are arm-bearing radials.
The fifth is a hexagonal " anal, 1 ' or (as I prefer to call it) azygos
plate, on the right upper edge of which rests a small arm-bearing
radial, while its left upper edge bears a smaller and true anal plate.
These characters are well shown in fig. I. a, which is a copy of
Billings's original diagram of the genus

and also in PL XI. figs.
3, 4, and 5, which represent the left, right, and anal sides of a
specimen from the upper part of the Trenton beds of Mercer
County, Kentucky, IT. S. A.
A form somewhat similar to Hybocrinus, though lacking the second
or true anal plate, had been described some years previously by Yon
Leuchtenbergt under the name of Apiocrinus dipentas (fig. I. b

Fig. I.
Calyx-diagrams of Hybocrinus and Baerocrinus.
a
CD E
b. Basal. r. Eadial. a. Anal plate.
A. Hybocrinus tumidus. After Billings.
B. H. dipentas, type. After Grewingk.
C, D. H dipentas, other varieties. After Schmidt.
E. Baerocrinus Ungerni. After Grewingk.

Report, Geological Survey of Canada, 1856, p. 274.
t Beschreibung einiger neuen Thierreste der Urwelt yon Zarskoje Sselo
(St. Petersburg, 1843, 4to.) p. 17, tab. ii. figs. 9 &