144 Miscellaneous. 
Thaumatocrinus is thus distinguished by four striking peculi- 
arities :— 
(1) The presence of a closed ring of basals upon the exterior of 
the calyx. 
(2) The persistence of the oral plates of the larva, as in Hyo- 
crinus and Rhizocrinus. 
(3) The separation of the primary radials by interradials which 
rest on the basals. 
(4) The presence of an arm-like appendage on the interradial 
plate of the anal side. 
Taking these in order— 
(1) No adult Comatula, except the recent Atelecrinus and some 
little-known fossils, has a closed ring of basals; and even in Afele- 
crinus they are quite small and insignificant. 
(2) In all recent Comatule, in the Pentacrinide, and in Bathy- 
crinus, the oral plates of the larva become resorbed as maturity is 
approached. In Thaumatocrinus, however, they are retained, as in 
Hyocrinus, Rhizocrinus, and Holopus, representatives of three diffe- 
rent familes of Neocrinoids. 
(3) There is no Neocrinoid, either stalked or free, in which the 
primary radials remain permanently separated as they are in Thau- 
matocrinus and for a short time after their first appearance in the 
larva of ordinary Crinoids. The only Palzeocrinoids presenting this 
feature are certain of the Rhodocrinide (as understood by Wachs- 
muth and Springer), e. g. Leteocrinus, Rhodocrinus, Thylacocrinus, 
&c. In the two latter, and in the other genera which have been 
grouped together with them into the section Rhodoerinites (W. and 
S.), there is a single interradial intervening between every two 
radials, and resting on a basal just as in Thaumatocrinus, But in 
the Lower Silurian Feteocrinus (of Billings, emend. W. and 8.) the 
interradial areas contain a large number of minute pieces of irre- 
gular form and arrangement. 
(4) It is only, however, in Reteocrinus and in the allied genus 
Xenocrinus, Miller, which is also of Lower Silurian age*, that an 
anal appendage similar to that of 7’aumatocrinus is to be met with. 
Of the four distinguishing characters of T’hawmatocrinus, therefore, 
one appears in one or perhaps in two genera of Comatule ; another 
is not to be met with in any Comatula, though occurring in certain 
stalked Crinoids; while the two remaining characters are limited to 
one family of the Palocrinoids, one of them being peculiar to one, 
or at most two genera which are confined tv the Lower Silurian 
rocks. 
Their reappearance in such a specialized type as a recent Comatula 
is therefore all the more striking.—Proc. Roy. Soc. 1883, No. 225, 
p. 138. 
* Reteocrinus occurs in the Trenton Limestone of Ottawa and in the 
Hudson-river group of Indiana and Ohio. -Xenocrinus has as yet been 
found in the latter group only. I cannot help suspecting that a better 
knowledge of this type will lead to its absorption into Reteocrinus,— 
PAG. 
ae 
