278 THE VOYAGE OF H.M.S. CHALLENGER. 



arms, however, for they bear the pinnules as their larger fellows do ; and in some forms 

 the lowest of them (tertiary arms) have a series of unequal axillaries and bear armlets on 

 their inner faces just as the large outer arms do. In such individuals these inner tertiary 

 arms are more equal in size to the outer pair. The two extreme types are well represented 

 on Tab. 97 of the Encriniden, figs. 5 and 6, by Quenstedt, who partially founds upon 

 them the distinction between the " Briariden " and the " Subangularen." In the former 

 group the inner tertiary arms are undivided armlets like those which come off farther out 

 on the ray ; while the inner tertiary arms of the Subangularen, though smaller than the 

 outer ones, bear armlets on their inner faces, which correspond to those on the inner faces 

 of the outer arms that spring from the same axillaries. 



Owing to the presence of these armlets on the inner tertiary arms, the Subangularen 

 generally have the " finger-reichsten Krone " as pointed out by Quenstedt. This is not 

 always the case, however, for in a specimen from the Posidonia-heds of Holzmaden, which 

 is figured by him,^ the inner tertiary arms are undivided, and their successors are more 

 equal to the outer arms of the ray than in some forms of Extracrimis hriareus. 



Under the name of Pentacrinus briareus imnutus, Quenstedt * has figured a curious 

 little species in which the division of the arms seems to be somewhat irregular, and the 

 distinction of arms and armlets less marked than is usually apparent in ExtrcLcrinus. 

 But I do not think that this variation, even if it be established, need have much effect 

 upon the stability of Extracrinus as a generic type. 



The differences between the Liassic and the recent Pentacrinidse on which the genus 

 was founded by the Messrs. Austin were at first regarded by the late Sir Wyville 

 Thomson as of merely subgeneric value. Believing that Pentacrinus hriareus " seems to 

 have a just claim to be recognised as the type of the genus Pentacrinus," he introduced 

 the name Cenocrinus for the Pentacrinus caput-Medusce of Miiller, and one or two fossils 

 which closely resemble it.^ He subsequently abandoned this name, however, and referred 

 the type to Pentacrinus as all later writers have done, some recognising Extracrinus as 

 a separate genus and some not. The Messrs. Austin^ pointed out that Miller "in his 

 arrangement of the Crinoidea has taken the PeMacrirnis caput-MeduscB for the typical 

 species, while at the same time his generic plate represents the dissected skeleton of quite 

 a different Crinoid. In the hope to remedy this intermingling of genera, we propose to 

 retain Miller's genus Pentacrinus, and to continue the Pentacrinus caput-Medusce as the 

 type of the genus;" while the name ^xiracnnws was proposed for the Liassic Pentacrinus 

 hriareus and Pentacrinus suhangidaris. This arrangement seems decidedly preferable 

 to that proposed by Sir Wyville, who eventually gave up Cenocrinus as a subgenus ; 

 though I cannot learn that he ever formally adopted Extracrinus. 



A second subgenus of Pentacrinus besides Cenocrinus was also proposed by Sir 



1 Encriniden, Tab. 101, fig. 1. - Ibid., Tab. 99, fig. 177. 



2 Sea Lilies, The Intellectual Observer, August 18G4, p. 3. * Monograph, p. 



