15 



must be their nature, are more prevalent near the outer margin 

 of the septal area, and in places are much broken up, as if 

 porous. On the whole, however, the general features of trans- 

 verse sections of the septa are so essentially those of Ethmoj)hyl- 

 lum, as exemplified in Mr. C. D. Walcott's figure of E. Whitneyi, 

 Meek,* Dr. Hinde's illustration of the same species, f and Prof. 

 F. von Roemer's representation of the Spanish E. marianum \ 

 that we must consider that the characters of the South Austra- 

 lian coral to be more in harmony with this genus than Archceo- 

 cyathus. 



The septa are very regular in appearance, of uniform width, 

 and equi-distant, presenting in these particulars a strong con- 

 trast to the crowded and somewhat irregular condition in 

 Archceocyathus. Furthermore they extend completely across the 

 septal area, as figured by Dr. Hinde, Mr. Walcott, and von 

 Roemer, and again, unlike those of Archceocyathus, do not stop 

 short of the inner margin, curve round, and unite with one 

 another. 



It has proved difficult to ascertain the number of septa, owing 

 to the imperfect condition of the calices, or the awkward angle 

 at which the natural section of the coral has been fractured. A 

 small specimen of Prof. Tate's possesses about twenty thick and 

 widely separated septa (PL III., fig. 10), and this is the least num- 

 ber I have observed. Between twenty on the one hand, and 

 forty-five, thirty-five, forty-nine on the other, but in some cases 

 these do not represent the complete cycles, the specimens being 

 imperfect. The septal area has an average width of from three 

 to four millimetres, but is so frequently cut in oblique section 

 that accurate measurements are difficult to obtain. 



The structure of the septa and the inner and outer laminse is 

 usually very compact, dense, and homogenous, and it is seldom 

 that any details can be made out. But in one horizontal section 

 certain peculiar appearances are present, in the form of small, 

 clear, circular spots in the substance of the septa, which can only 

 be explained on the supposition that they are either vertical 

 tubuli or pores passing through the septa obliquely. Another 

 section, taken from a specimen from Wirrialpa, shows decided 

 evidences of a secondary deposit in the form of a lining of clear 

 calcite following the outline of each interseptal loculus, easily dis- 

 tinguished from the denser material of the septa, and with a 

 more or less undulating margin (PI. II.. fig. 1). 



The inner and outer lamina, or wall-plates, have exactly the 

 same structure as the septa. The former is, however, much 



*Bull. U.S. Geol. Survey, 1886, No. 30, t. 4, f. MA. 

 t Quart. Journ. Geol. Soc, 1889, xlv., t. 5, f. 7. 

 + Lethasa Geognostica, loc cit, p. 300, f. 556. 



