16 



broken up, probably from its perforate nature, as described by 

 Dr. Hinde, both in ArcJimwyathus and Ethmojohyllum. The 

 inner lamina, on the contrary, entirely departs from the ArchcHo- 

 cyafhiis-type, and closely follows that of EtluaophyUuin. In the 

 former it is delicate, and directly " perforated by closely set cir- 

 cular apertures regularly arranged in quincunx." In the latter, 

 however, this inner lamina " consists of a series of relatively large 

 canals directed obliquely upward and inward, so that in transverse 

 section they present the appearance of one or more rows of 

 vesicles cut across." This is tlie fundamental difference between 

 the two genera, and is precisely the structure we have presented 

 in the South Australian fossils. In PI. II., figs. 3 and 4, the 

 septa will be seen to dissolve into a single, or at the utmost a 

 double row of irregular or partially-preserved vesicles. It will, 

 therefore, be apparent that the fossils now under description 

 must be referred to EtUmophylhim rather than ArcluHOcyathus. 



Dr. Hinde describes the outer wall-plate as protected by an 

 epithecal lamina, apparently non-perf orate, in Archceocyathus; 

 but mention is not made either of its absence or presence in 

 EthmophyUnm. I have quite failed to detect any non-perforate 

 epithecal layer, a point in w4iich the present specimens resemble 

 the Sardinian Arclueocyathiis examined by Dr. Hinde ; this may 

 be, however, a mere matter of preservation. 



With the view of confirming the reference here made to 

 Etlimophyllum, a comparison may advantageously be made of the 

 cross section of the inner lamina-tubes of PL 11. , fig. 4, with Mr. 

 Walcott's figure"^ of the same structure in E. Whitney i ; our 

 illustration of dissepiments with his figuref of these divisions in 

 the same species ; and lastly, the secondary deposit investing the 

 septa in PI. II., fig. 1, with their clothed condition in another of 

 the same author's figures [j; of E. Whitney i. 



In dealing with fragmentary material such as the present it is 

 very difficult to limit the characters on which specific separation 

 can be based, but it is possible that two species may be differen- 

 tiated on the size, form, and number of the septa. For instance, 

 the dissimilarity visible in the structure of PI. III., fig. 10, with 

 its small corallum and few and widely-separated septa, with that 

 presented by PI. II., figs. 2 and 3, may be specific ; but so much 

 variation in the number of the septa has been noted that, for the 

 present, the specimens had better be regarded as forming one 

 species only, under the name of Ethmophyllum Hindei. 



As here defined E. Hindei has been found at Kanyka (PL II., 

 fig. 2), the Blinman ^Pl. 11. , tig. 3), and at Wirrialpa (PL II., 



% !)• 



'■' Bull. U. vS. Geol. Survey, 1886, No. 30, t. 4, f. 1 r. 

 \Loc. cit., t. 4, f. 1 h. 

 XLoc. cit., t. 4, f. 1 e. 



