77 
sometimes rolling ; incomplete give rise to lenticular or wedge-shaped 
vesicles, true blister- cysts absent ; tabulae may, or may not, support longi- 
tudinal spines on their upper surfaces. Gemmation where known copious, 
simple or compound-calicular, and frequently rejuvenescent; possibly also 
parietal. 
Thyplasma Lonsdalei, Lth.fil. 
(Plate X; PI. XI, Figs. 2-4 ; PI. XII, Fig. 1 ; PI. XIX, Fig. 4; PI XXV, Fig. 5; 
PI. XXVI, Figs. 1-7.) 
Tryplasma Lonsdalei, Etli. fil., Rec. Geol. Survey N. S. Wales, 1890, II, Pt. 1, p. 15, t. 1. 
Specific Characters. — Corallum of loosely aggregated to sub-fasciculate 
groups of corullitcs, sometimes forming large colonies, at least six inches in 
height. Corallites long, slightly tlexuous, cylindrical, gradually increasing 
in size upwards to an average diameter of six millimetres, but attaining as 
much as eight, here and there united laterally either by fusion of their Avails, 
or by fistulse ; bases pointed ; length at least six inches. Epitheca delicate, 
concentrically lined, the lines crenulated on passing over the rugae. 
Fistula? Avell developed, usually more or less horizontal, present in all parts 
of the corallum, and only rarely passing from corallite to coral life on the 
same level ; swollen at their junction with the corallites, and at times provided 
with a few septal spines ; semi-fistulae as knobs or small disconnected 
processes. Septal lamellae narrow, forty to fifty in a cycle, primary and 
secondary ; spines tliorn-like, long, projecting inwards for about one-third 
the diameter of a corallite, from one to four cycles between tabulae, but more 
commonly three, sometimes with lateral denticles. Tabulae numerous and 
usually complete, generally regularly spaced apart, but here and there 
groups of close set floors, horizontal, oblique, or concave, often displaying a 
slight, central depression ; incomplete vesicular tabulae rare, but when 
present small, triangular and usually marginal. Gemmation compound- 
calicular-rejuvenescent, two buds immediately diverging from one another. 
Observations . — This species must be regarded as the Australian type, 
as it Avas first described. It need not be mistaken for any other species 
except T. vermiformis ; the distinctive features are referred to under the 
latter. The specific points of importance in T. Lonsdalei are : — 
(1) Eorm of the corallum. 
(2) Frequent occurrence and length of the fistuhe. 
(3) Abundance of the septal lamellae, size of the spines, and presence 
of lateral denticles. 
(I) Grouping of the tabulae. 
