especially as some of the fragments lie in reversed positions 

 to each other. The arm-fragments are imperfect at each 

 extremity, so that it is impossible to define the position which 

 they severally occupied in the crown. The largest example, 

 present, has a length of 2 in. The lower portion of this 

 fragment consists of five ossicles, each deeply niched at half 

 distance. An axial joint marks the beginning of bifurcation 

 (the only one seen on the slab), beyond which the brachial 

 ossicles are somewhat reduced in size, but are equal to each 

 other in the respective branches, and destitute of the 

 divisional niche seen in the plates below the point of bifurca- 

 tion. There are 28 brachials in one branch and 35 in the 

 other — neither are complete. 



In the case of the lower limb (below bifurcation) the 

 ossicles measure one-tenth of an inch in diameter, but those 

 in the limbs above the axial joint gradually taper to a fourth 

 of the original size. This would lead us to infer that the 

 specimen shows the last fork in the arm and the respective 

 rays, thus formed, would be finials. All the arm-fragments 

 seen on the stone are closely pinnulated, and the latter extend 

 along the entire length of those exposed. 



The specimen agrees with the genus Isocrinus in the 

 characteristic feature of its isotomous bifurcation, but is 

 distinguishable from Isocrinus australis by its relatively 

 small size. The type specimen has been placed m the National 

 Museum, Adelaide. 



DESCRIPTION OF PLATE I. 



(All objects of natural size.) 



Figs 1 and 2. Isocrinus australis (Moore). Pseudomorphs in 

 precious opal. The light-coloured portions show the opaline 

 interior where the surface "skin" has been removed by abrasion. 

 The darker portions represent the ferruginous coating of the 

 specimens. 



Fig. 3. Isocrinus parvus, n. sp. Brachia, probably finials, 

 showing pinnules and isotomous bifurcation. 



