88 
as a number of comparatively small discs, the latter representing one or more 
of the old visceral chambers. Another important feature is the plane even 
surface of the tabulae on fracture, arising from the shortness of the septal 
spines. This character T. deniroidea bears in common with T. congrega- 
tionis; indeed it is, in many ways, closely allied to the latter, and, had it not 
been for the marked development of the hstulae, lesser number of septal 
lamellae in a cycle, and presence of vesicular tabulae in the latter, I would 
have felt inclined to unite the two forms. 
I am not acquainted with the mode of reproduction in T. columnaris , 
but, over and above this, the present species is separated from that coral by 
the regularity of its tabulae, the absence of accretion ridges to any degree 
of importance, and generally less robust appearance. 
The principal characters of T. dendroidea are : — (1) Mode of growth ; 
(2) preponderance of complete tabulae ; (3) extent of surface of the latter on 
fracture. 
T. ( Amplexus ) stigmatophorus , Sandb.fr., 1 from the Devonian of 
Nassau, is probably allied here, having the same large complete tabulae, 
with peripheral septal spine impressions. 
Localities . — Derrengullen Creek, a branch of the Yass Diver, Portion 
10, Parish Yass, County King (C. Cullen and IV. S. Dun — Mining and 
Geological Museum; A. J. Shearsby — Australian Museum) : Barber’s Creek, 
a branch of Derren-gullen Creek, Parish Yass, County King (A. J. Shearsby — 
Australian Museum. 
Tryplasma derrengullenensis, sp. non. 
(Plate XXII, Figs. 5-8.) 
Specific Characters. — Corallum simple. Corallites solitary, small, 
turbinate, ob-conical, or elongate and twisted, irregularly undulated in 
consequence of the unequal development of bourrelets. Radiciform processes 
well developed, always on one side a corallite more than the other, clustered. 
Epitheca complete, ornamented by scalloped encircling lines. Rugae broad. 
Bourrelets prominent for so small a species, representing the margins of pre- 
existing corallites. Calice deep, nearly straight-walled ; floor flat. Septal 
lamellae very numerous and short, primary and secondary, the former leaving 
deep furrows in casts, the latter shallow ; spines thorn-like, the primary much 
larger than the secondary, one to two cycles in old visceral chambers, and 
: Sandberger, fr. — Verstein. Rhein. Schich. Nassau, Lief. 8, 1854, t. 36, f. 146. 
