176 Dr. H. A. Nicholson and Mr. E. Etheridge, Jun., on 



drical or flattened branches, which have a diameter of from 

 less than 2 to more than 3 centim. Corallites approximately 

 vertical in the centre of the branches, but finally bending 

 outwards nearly at right angles. In the central portion of 

 the corallum the tubes are thin-walled and polygonal ; but in 

 the peripheral part of their course they are annulated by perio- 

 dical thickenings of the wall separated by untliickened seg- 

 ments, and they are here snbpolygonal. The average diameter 

 of the tubes is about ^ millim. The tabular are few and 

 remote, and for the most part placed at corresponding levels 

 in contiguous tubes ; they appear to be sometimes complete, 

 but they seem at other times to be perforated by a central 

 aperture. Acanthopores wanting. 



Ohs. As before mentioned, this species so closely resembles 

 the Strzeleckian type of S. ovata, Lonsd., that we thought 

 ourselves justified in placing it under the latter species. In its 

 minute structure, however, it differs widely from S. ovata^ and 

 resembles no other species of the genus known to us. One of 

 the most marked characters of S. australis, in which it seems 

 to stand alone among the species of Stenopora, is the total 

 absence of acanthopores (PI. III. fig. 5). This character at 

 once distinguishes the species from iS. ova^a, Lonsd. It agrees 

 with the latter in the fact that the walls of contiguous coral- 

 lites are completely amalgamated, the primordial wall only 

 being visible in the axis of the brandies, and also in the 

 average size of the tubes ; but the corallites are mostly more 

 of a polygonal than of a simply rounded shape. As seen in 

 longitudinal sections (PL III. fig. 6) the corallites are thick- 

 ened periodically in the peripheral region of the corallum by 

 very regular fusiform thickenings placed at corresponding 

 levels in contiguous tubes, as are also the tabula?. As seen in 

 long sections the tabulae appear to be complete; but as viewed 

 in tangential sections appearances are seen wliich are difficult 

 to explain except upon the supposition that the tabulge are 

 perforated by a central aperture (PI. III. fig. 5). Thus in 

 many of the corallites, as seen in tangential sections, we ob- 

 serve a broad ring of light-coloured sclerenchyma internal to 

 the proper walls of the tube and enclosing a central rounded 

 aperture. What this ring is, unless it be a perforated tabula, 

 it is difficult to see ; but there is the curious feature that it is 

 usually separated from the true wall for a portion of its extent 

 on one side of the tube. 



In our former description of this species {loc. cit.) we de- 

 scribed and figured the above-mentioned singular structures, 

 but were unable to give any explanation of their nature, as 

 we believed the tabulas to be imperforate. We are obliged to 



