13 



features of the organisms to advantage. The Wirrial2Da speci- 

 mens, on the contrary, from their similarity to the colour of the 

 limestone are difficult to discern at a first glance, a difficulty 

 which is increased by the large number of fragments present of 

 the broken-up wall. 



In the Ardrossan limestone the corals are usually seen in sec- 

 tion, and show to advantage from the white colour of their walls 

 and tissue as compared with the colour of the matrix. I have 

 not examined any very complete individuals from this rock, and 

 from its peculiar semi-conchoidal fracture it is not easy to obtain 

 sections along any given well-defined line. A few weathered-out 

 examples have been examined from Kanyka, and these have 

 yielded good results, but in the majority of cases information has 

 been gained chiefly through sections. 



Measurements are rendered difficult from the various ansies at 



o 



which the corallum.s are naturally cut by the fracture or weather- 

 ing of the matrix. Taking the specimens irrespective of genus, 

 an imperfect corallum from Wirrialpa is one and three-quarter 

 inches long, and another seen in section from Ardrossan measures 

 one and a half inches in its longest diameter, slightly obliquely. 

 An imperfect calyx from the former locality is one and a quarter 

 inches in diameter, but others from the latter are much larger, al- 

 trrs^'h some which appear in transverse section in the limestone 

 possess a diameter of half an inch or slightly more, and this is a 

 common measurement. An example from Wirrialpa differs from 

 most of the others in having a markedly oval section, the longest 

 diameter being one inch and the shorter three quarters of an inch. 

 A more perfect fragment from Kanyka, three quarters of an inch 

 in length, has a diameter at one end of half an inch, and at the 

 other measures three-eighths. A well-preserved little corallum in 

 Prof. Tate's collection, three quarters of an inch in length, pos- 

 sesses a diameter of a quarter of an inch, and, judging from the 

 number of the septa is the most rudimentary form I have seen. 



From these figures we learn that the South Australian speci- 

 mens, on the whole, are of less size than the Canadian Archwo- 

 cyatkus, although one or two examples are quite as tall as the 

 former, but fall short in the diameter of their calices.* Similarly 

 they are undoubtedly shorter than the type specimen of Ethmo- 

 johyllum, E. Whitneyi, Meek,t in which the corallum reaches as 

 much as six or more inches in length, and again shorter than the 

 Spanish species of the last-named genus, Etlimophyllum mari- 

 anum, Roemeri, but the largest from Ardrossan, and the larger 



-"Bull. U.S. Geol. Survey, 1886, Xo. 30, p. 72. 

 i-Ibid, t. 4, f. 1. 



:I:Lethi«a Geoguostica, Theil 1, Lethasa Palasozoica, 1 Lief., 1880, p. 301. 

 f. ooa. 



