APHKOPHYLLUM HALLENSE AND LITHOSTROTION. 61 



The Australian Species. 



The Australian species before me, namely those from 

 New South Wales and Queensland, agree in all their essen- 

 tial characters with their European congeners. Yet as a 

 group they present certain distinctive characters. 



Tabulce. — The most striking difference between the 

 Australian, both New South Wales and Queensland, and 

 the British forms is that in the tabular tissue. Here, 

 smaller, much more arched and less regular plates (tabellae) 

 take the place of the larger more regular conical tabulae 

 characteristic of the British columate species, cf. figs. 3 

 and 6, Plate IV. A few forms do not show this character 

 so strongly developed, as for example, the corallite repro- 

 duced in fig. 6, Plate III. I have noticed a tendency to 

 this development among British forms, but never to the 

 same degree. 



The replacement of tabulae by tabellae is an interesting 

 feature; it marks an intermediate stage in the evolution 

 of a clisiophylloid form, i.e. one in which there is a central 

 axial structure built up of tabellae (the "Central Column") 1 

 distinctly differentiated from the rest of the tabular tissue 

 which surrounds it. A clisiophylloid derivative of the 

 Ldthostrotion stock has been recorded by the author from 

 Northumberland and described by the late Arthur Vaughan. 2 



Columella. — The stout columella is a very noticeable 

 feature common to the Australian species, and distinguishes 

 them as a group from the British type in which this axial 

 rod is not usually so pronounced, and is often, in fact, 

 weakly developed. 



Dissepiments. — The dissepiments are larger and less 

 regular than those characteristic of British species. 



1 Q.J.G.S., Vol. lxix, (1913) p. 59. 



2 Trans. Nat. Hist. Soc, Northumberland, N.S. Vol. in, 1910, p. 606 

 and 631, pi. xvi, fig. 10. 



