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 Hxtracrinus 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 Hxtracrinus, 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 Miller, 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 Extracrinus, 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 a 
of the first series of perisomic plates in Hatracrinus, not only with the pelvis or dors 
central plate of Pentacrinus, but also with the outer circlet of basals in Hnerinus ; while 
the five small, nearly concealed pieces forming the so-called dorsocentral plate of 
Eextracrinus, 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 briareus 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 Hnerinus 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. Hncrinus, like Kxtracrinus, has a dicyclic base; 
but the same tendency to downward prolongation of the radials is seen in Pentacrinus 
naresianus (Pl. XXX. fig. 1) and more distinctly in Metacrinus (Pl. XXXIX. fig. 1; 
Pl. XLIX. fig. 2). 
The Austins’ genus Hztracrinus has not met. with the attention which it deserved, 
