HALYSITES IN NE"W SOUTH "WALES — ETHERIDGE. 79 



corals, still sufficient details can be made out to elucidate the 

 finer characters of our Halysites. 



The mineral condition is very remarkable. The corals are 

 preserved in a dark blue limestone, the tissues where unaltered 

 being composed of the usual dark grey or brown sclerenchyma, 

 the general infilling of all the intertabular spaces or old visceral 

 chambers, being crystalline or granular calcite, the former in 

 places with cleavage. Every here and there, however, the walls 

 of the corallites are converted into a radiating siliceous mineral, 

 or blebs of the same look as if forced into the walls ; there is 

 every reason to believe that the latter is chalcedony, in the form of 

 Beekite rosettes, a by no means uncommon mineral in our Lower 

 Palaeozoic Invertebrata. In some cases these blebs occupy spaces 

 within the corallites, breaking up the uniformity of the tabulate 

 structure in a very marked manner. 



Notwithstanding this excessive alteration the external walls 

 are quite discernible, and here and there the continuous epitheca 

 on both the free sides of the laminje is visible also. As described* 

 by Nicholson, the epitheca does not take any part in the " form- 

 ation of the partition which actually divides any tube from its 

 neighbour on either side," but the partitions are formed solely by 

 the coalescent tvalls of the two contiguous corallites." Further- 

 more, the corallites are of two orders, as in the well known 

 Halysites catenulatus, Linn., thus at once distinguishing it from 

 H. escharoides, Lamk. The larger, or normal corallites are oval, 

 from three-quarters to one mm. in longest diameter, and the latter 

 in the direction of the chain. In a macroscopic examination these 

 may be at once distinguished by an outward bulging of the 

 epithecated walls. The smaller corallites, or those of the second 

 order, are ranged alternately with the larger, and are either round 

 or quadrate, and each is enclosed by a thick wall of its own, 

 distinct from the common or enclosing wall of the laminje. The 

 position of these " interstitial tubes," as they are termed by 

 Nicholson, is equally discernible externally by a biconcavity of 

 the wall opposite to each secondary corallite. The angles of 

 junction of any two lamina? that assist in forming a reticulation, 

 or fenestrule, are always occupied by an interstitial corallite, which, 

 in well weathered specimens, is visible with an ordinary pocket 

 lens. Septa are absolutely wanting. 



The two sets of corallites become even more apparent in a 

 vertical section. The normal tubes are closely tabulate, the 

 tabulae horizontal, very regular, and equidistant, five in the space 

 of one mm., enclosing between them more or less transversely 

 elongated or quadrangular intertabular spaces. The interstitial 

 tubes, on the other hand, are very narrow and pipe-like, sparsely 



* Nicholson— Tab, Corals Pal. Period, 1879. p. 227. 



