294 



ZOANTHARIA. 



and in Palceocyclus porpita, the corallum is so short that neither dis- 

 sepiments nor tabulae are developed at all.] The septa are thickened 

 with stereoplasma (fig. 127, b and c), and are not " carinate." As 

 a rule, the septa are of two orders, alternately long and short. In 

 all the typical members of the section, the symmetry is conspicu- 

 ously bilateral, and a tetrameral disposition of the septa can usually 

 be readily determined. There is generally a well-marked fossula 

 (fig. 1 7 2,/), placed dorsally and containing the "cardinal septum "; or 

 ventral in position, enclosing the "counter septum"; or rarely lateral 

 and traversed by one of the " alar septa." In some forms a fossula 

 is not determinable (e.g., in some species of Streptelastna and in 



Li?idstr(z?nia generally). In the 

 genera just mentioned it is also 

 usual for the lower part of the 

 visceral chamber to be more or 

 less largely filled up with a de- 

 posit of stereoplasma. The Zaph- 

 rentoid Corals are exclusively 

 Palaeozoic, and range from the 

 Ordovician to the Carboniferous 

 period, or, if the genus Polyccdia 

 be admitted here, to the Permian. 

 Family 1. Zaphrentidce. — The 

 typical family of the Zaphrentoid 

 Corals is that of the Zaphrentidce, 

 of which the genus Zaphrentis 

 itself is the central form. The 

 family is characterised by the 

 marked bilaterality of the coral- 

 lum, a well-developed fossula be- 

 ing present, while the develop- 

 ment of the septa is usually char- 

 acterised by the inequality in size 

 of certain of these structures. 

 The septum which occupies the 

 fossula may be either the " car- 

 dinal septum " or the " counter 

 septum," but in either case it is 

 shorter than the other long septa. 

 Neither a true columella nor a pseudocolumella are developed, and 

 there is a thick theca formed by the coalescence of outgrowths from 

 the outer ends of the septa (fig. 172, c). It is doubtful if a true 

 epitheca is present. 



Only the more important of the genera of the ZaphrentidcE can be here 

 noticed, the chief being Zaphre?itis itself. In this genus (fig. 173) the 



Fig. 173. — Zaphrentis cornicula, the wall: 

 of the calice broken away, and snowing th< 

 " fossula," of the natural size. Devonian 

 America. (Original.) 



