92 
Let ns now tnrn onr attention to what I have termed decorticated, or, 
perhaps it should more correctly speaking he decalcified casts. In snch 
instances, the major portion of the snhstance of the plate has gone, leaving 
the concentric and radiating lines hehind, possibly from a different chemical 
composition to the remaining portion of the plates. Snch casts are seen in 
onr PI. XV, Pigs. 5-8, and are always accompanied hy a hollow space above 
them representing the thickness of the removed plate snhstance. Thronglithe 
exertions of Mr. B. G. Engelhardt, of the Public School, Jamheroo, I am able 
to demonstrate the presence of this ornament on the interior, rather than the 
exterior of plates. PI. XXII, Pig. G, represents the exterior 
of one of the hasals of T. Clarkely whilst Pig. 7 of the same plate shows the 
interior of this plate. The former is plain and without scnlptnre, the latter 
exhibits the described markings in an excellent manner. Again, PI. XXII, 
Pig. 8, is the convex exterior of another plate, probably one of the radials^ 
of the same species ; whilst PL XXII, Pig. 9, is its interior, in Avhich, if 
anything, the sculpture is more strongly marked than on the inner surface of 
the basal plate. In his earlier description of the Australian fossils, collected 
hy the Wilkes’ United States Exjdoring Expedition, Prof. Dana described the 
fossils called Feutadia as with “ one side quite smooth, the other delicately 
and closely marked with parallel siihcrenulate ridges, having the angles of a 
regular pentagon and concentric.”'^ It may, therefore, I think, he accepted 
that this form of sculpture in Tribrachiocrinus is confined to internal casts 
and decorticated plates. 
PI. XV, Pig. 6, is the heptagonal basal, one of the angles of the 
heptagon being hid hy the overhanging matrix ; Pig. 7 of the same plate is 
one of the hexagonal hasals ; whilst Pig. 8 is the left non-arm-bearing 
anterior radial. As regards Pig. 5, 1 am somewhat in doubt, it may he either 
the left anterior basal of T. Clarkei, or the hexagonal anal-supporting 
basal of Fhicdocrinus KonincM, and I am inclined to believe the latter from 
the strong radiating ridges, which coincides with the structure of Dana’s 
Fentadia corona. 
A hasty glance at the basal plate portrayed in PI. XXII, Pig. G 
would lead one to regard it as the three infra-hasals anchylosed, especially 
the appearance of the almost central depression, resembling that of the 
columnar scar. The figure of the interior (PI. XXII, Pig. 7), hoAvever, 
' The edges being broken, it is difficult to trace the exact form. 
^ American Jouru. Sci., 1847, IV, p. 152. 
