342 P. M. DTJNCAN ON" SOME FOSSIL REEE-BTTILDING CORALS 



was, and is at the present day, a reef-building and not a deep-sea 

 group. Thamnastrcea, so common in the Jurassic ages, was then a 

 reef-builder and a littoral form, and after a great number of species 

 had been evolved, it became rare in the Nummulitic period, and 

 died out in the subsequent geological age in the Australian region, 

 having been probably destroyed in the European areas by the 

 changes which ensued upon the destruction of the Eocene reefs. 

 List of species from Table Cape, Tasmania : — 



1 . Dendrophyllia epithecata, nobis * 



2. Heliastraea tasmaniensis, sp. nov. 



3. Tkamnastraea sera, sp. nov. 



Genus Heliastrjea. 



Heliastraea tasmaniensis, sp. nov. Plate XXII. figs. 1-3. 



The corallum is incrusting, and the corallites are subcylindrical 

 and distant. The calices project but slightly, and differ much in 

 size ; the fossa varies in depth, being in some instances slight and 

 in others more than equal to the diameter of the calyx ; and the 

 margin is thin. The septa are alternately long and short, are 

 straight and thin, and are marked with separate granules or with 

 linear groups of them. They are not exsert, and are only slightly 

 thicker at the wall than elsewhere : their arrangement is irregular ; 

 for in the largest corallites there are four cycles in six systems, and 

 a few members of the fifth cycle in one or two also, whilst in the 

 majority the fourth cycle is incomplete, there being three cycles in 

 six systems, and in one or two members of the fourth. In some 

 calices the quaternary arrangement of the septal numbers exists, 

 there being only four primaries and four cycles in four systems. 

 The distinction between the primary and secondary septa is slight ; 

 but the existence of a very small septum between two much larger 

 ones is very decided. The large septa reach far inwards and are entire. 

 The columella is very small, and is formed of trabecule between the 

 septal ends. The wall is thin, and in some instances more so than 

 are the larger septa. The endotheca is largely developed, and the 

 dissepiments are thin, long, and curved downwards. 



The costse of the large septa are well developed ; and they are 

 either long and wavy over the ccenenchyma, or are short and re- 

 stricted to the corallite ; those of the small septa are rudimentary, 

 and exist either as faint projecting lines or as spines ; and their pre- 

 sence between the more prominent ones is very marked ; they are 

 all thin and delicate. The exotheca is greatly developed and is 

 largely cellular, the direction of the upper parts of the cells being 

 nearly horizontal ; but all parts of it, including the vertical partitions, 

 are thin. 



The diameter of the calices is under i inch, and their distance 

 apart is rather more or slightly less. 



The species is remarkable for the tenuity of the whole of the struc- 



* Quart. Journ. Geol. Soc. vol. xxxi. p. 677. 



