REPORT ON THE CRINOIDEA. 275 



the elements of the so-called dorsocentral plate, were described by the Messrs. Austin as 

 " solid pointed pieces, whose points pass outward, and rest on the salient angle of the 

 pentagonal column," precisely, in fact, like the rays of the stellate dorsocentral plate or 

 pelvis of Pentacrinus asterius, with which Miller had rightly regarded them as 

 homologous. The Messrs. Austin, however, supposed Miller to have been in error upon 

 this point, as they believed the so-called dorsocentral plate of Extracrinus to be 

 homologous with that of Pentacrinus, not paying any attention whatever to its position 

 with regard to the radial symmetry of the animal. Neither did they notice that in 

 Pentacrinus the five elements composing the dorsocentral plate are perforated by bifur- 

 cating canals, which occur in Extracrinus, not in the component pieces of the dorso- 

 central plate, but in those of the next series, the pelvis of Miller ; and they were conse- 

 quently led to regard these last, the basals of Miillcr, as representing the first series of 

 perisomic plates (or the first radials, Miiller) of Pentacrinus ; while the first radials of 

 Extracrinus, alternating in position with the basals, were described by them as a second 

 series of lateral or perisomic pieces which are unrepresented in Pentacrinus. The fact is, 

 however, that it is the dorsocentral plate of the former genus which is not represented 

 in Pentacrinus, the pelvis of which represents the so-called first series of perisomic plates 

 in Ext7'aci'inus, as was rightly supposed by Miller. The two sets of plates are precisely 

 similar in their position relatively to the radial symmetry of the animal and in being 

 perforated in the same way by bifurcating canals. These two important points, which 

 were entirely left out of consideration by the Messrs. Austin, demonstrate the homology 

 of the first series of perisomic plates in Extracrinus, not only with the pelvis or dorso- 

 central plate of Pentacrimis, but also with the outer circlet of basals in Encrinus ; while 

 the five small, nearly concealed pieces forming the so-called dorsocentral plate of 

 Extracrinus, which alternate with the true or outer basals, obviously represent the inner 

 circlet of basals of Encrinus. The Messrs. Austin were fortunate enough to obtain 

 a specimen of Extracrinus hriareus showing the interior of the calyx, the centre of the 

 floor of which is occupied by the five small, radially placed elements of the so-called 

 dorsocentral plate ; and the resemblance in every respect between these and the inner 

 circlet of basals in Encrinus is so close as to leave little doubt that they are homologous 

 with one another. 



It is therefore somewhat striking to find that the extensive downward prolongation 

 of the first radials over the upper stem-joints, which is the chief characteristic of 

 Extracrinus, as defined by the Messrs. Austin, is also found, though to a smaller extent, 

 in Encrinus, as pointed out by Beyrich. Encrinus, like Extracrinus, has a dicycHc base ; 

 but the same tendency to downward prolongation of the radials is seen in Pentacrinus 

 naresiamis (PI. XXX. fig. l) and more distinctly in Metacrinus (PI. XXXIX. fig. 1; 

 PL XLIX. fig. 2). 



The Austins' genus Extracrinus has not met with the attention which it deserved, 



