274 THE VOYAGE OF H.M.S. CHALLENGER. 
fact, the first of these, Pentacrinites vulgaris, designates a fossil type to which he also 
referred (under the name of Encrinus caput-Meduse) the recent specimens described by 
Guettard and Ellis. These were subsequently referred by Miller to his Pentacrinus 
caput-Meduse (= Pentacrinus asterius, Linn, sp.) ; and the type was eventually rendered 
classical by the researches of Miiller. Under these circumstances I see no reason for 
departing from the practice of d’Orbigny, Forbes, Pictet, de Loriol, and Zittel, and have 
therefore attributed the genus to Miller, with the date 1821. When establishing it, 
he simply converted into a generic designation the name which had long been commonly 
employed for fragments of stems with the characteristic petaloid markings on their 
terminal faces. Miller’s generic diagnosis of this type, like those of the numerous other 
Crinoids described by him, corresponds to the definition of a family, when considered by 
the help of our present knowledge. 
Five species were established by Miller'—(1) the recent Pentacrinus caput-Meduse 
from the West Indies; (2) the two fossil species from the Lias, Pentacrinus briareus 
and Pentacrinus subangularis; and (3) two other fossils which need not be considered 
here. Although apparently taking the single recent species then known as the type of 
the genus, he gave a generic diagnosis which represents, although imperfectly, the 
dissected calyx of one of the two Liassic species. These have the radials prolonged 
downwards over the upper stem-joints between and below the outer ends of the basals ; 
and the Messrs. Austin consequently proposed to establish the new genus Hxtracrinus 
for their reception, while restricting Pentacrinus to species having the general character 
of the recent Pentacrinus caput-Meduse (= Pentacrinus asterius, Linn, sp.). 
Miller described the “ pelvis” of the fossil Pentacrinus briareus and Pentacrinus 
subangularis as similar in character to that of the recent Pentacrinus asterius, namely, as 
consisting of five small and nearly cuneiform basals in contact by their central ends. 
The Messrs. Austin, in accordance with their peculiar method of nomenclature, gave the 
name “dorsocentral plate” to the pelvis of Miller (basals, Miiller) ; and they described 
that of Pentacrinus asterius as “resembling an enlarged and thickened supracolumnar 
joint,” without divisions, the salient angles of which alternate with the five first 
radials, or, as they called them, the first series of perisomic pieces. The pelvis of the three 
fossil species Pentacrinus johnson, Pentacrinus tuberculatus, and Pentacrinus milleri, 
was described as closely resembling that of Pentacrinus asterius; but in their diagnoses 
of Extracrinus briareus and Extracrinus subangularis they differed considerably from 
Miller and Goldfuss. They gave the name dorsocentral plate, not as usual to the pelvis 
of Miller as in Pentacrinus asterius, but to five small and nearly concealed pieces which 
are placed beneath the true pelvis, and were unknown to Miller. They are radial in 
position, and not interradial like the pieces described by Miller and Goldfuss as composing 
the pelvis of these two Liassic species. These, the true basals, which thus alternate with 
1 A Monograph on Recent and Fossil Crinoidea, Bristol, 1843-45, p. 95. 
