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-Meduscp) the recent specimens described by 

 Guettard and Ellis. These were subsequently referred by Miller to his Pentaci'inus 

 caput-Medusce { = 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-Medusce 

 from the West Indies ; (2) the two fossil species from the Lias, Pentacrinus hriareus 

 and Pentacrimis subangidaris ; 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 Extracrinus 

 for their reception, while restricting Pentacrinus to species having the general character 

 of the recent Pentacrinus caput-Medusce { = Pejitacrinus asterius, Linn, sp.). 



Miller described the " jielvis " of the fossil Pentacrinus hriareus and Pentacrinus 

 suhangularis 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 Pentctcrinus johnsoni, Pentacrinus tuherculatus, and Pentacrinus milleri, 

 was described as closely resembling that of Pentacrinus asterius ; but in their diagnoses 

 of Extracrinus hriareus and Extracrinus siihangularis 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 

 ' A Monograph on Recent and Fossil Crinoidea, Bristol, 1843-45, p. 95. 



