SUBCLASS I 



TETRACORALLA 



81 



cardinal septum (Fig. 100, h), and takes up a position parallel with the alar 

 septum. This leaves an intermediate space between the cardinal and the 

 newly formed septa, which becomes filled, however, by the repeated insertion 

 of new septa one above the other in the same manner as the first ; and hence 

 they diverge from the cardinal septum, as they grow upward, in a pinnate 

 fashion. Likewise the two counter quadrants lying between the alar and 

 counter septa become occupied by lamellae which are given off from the alar 

 septa, and gradually arrange themselves parallel with the counter septum. 

 The mode of growth in the Tctracoralla will be readily understood on inspect- 

 ing the surface of those specimens, the septa of which are visible on the 

 exterior, or where the wall is readily removed by corrosion or polishing. One 

 may then note three distinct lines extending from the calicinal margin to the 

 base ; these mark the cardinal and the two alar septa, from which the other 

 pinnately branching septa are directed obliquely upward (Fig. 101). The 

 order in which the septa are given 

 off in the four quadrants, according 

 to Kunth, is indicated by the 

 numerals in Fig. 100. 



Many of the Tetracoralla multiply 

 only by sexual reproduction, and occur 

 only as single individuals ; asexual 

 reproduction takes place usually by 

 calicinal, more rarely by lateral gem- 

 mation, and results in dendroid or 

 massive colonies. 



Dissepiments are generally abund- 

 antly developed between the septa, 

 which latter are compact, and the 

 upper edges of which are either 

 smooth or serrated. Sometimes the 

 dissepiments fill the whole interior 

 with a vesicular tissue, and the 

 central visceral cavity is frequently 

 entirely partitioned off by horizontal, 



inclined or funnel-shaped tabulae. The Wall is usually composed of the 

 thickened and fused septal edges ; sometimes it is invested with epitheca 

 and furnished with vertical rugae or root-like processes. A true coenenchyma 

 is absent. In a few genera the calice is provided with a lid or operculum, 

 which may be composed of one (Calceola) or of several plates (Goniophyllum). 



With the exception of a few genera the systematic position of which is 

 uncertain, all the typical Tetracoralla are confined to the Paleozoic rocks. 



Fig. 100. 



Menopli yll am tenuimnr- 

 ginatinn B. and H. Car- 

 boniferous Limestone ; 

 Tournay, Belgium. 2/j. 

 h, Cardinal septum ; g, 

 Counter septum ; s, Alar 

 septa. 



Fig. 101. 



Streptelasma profundum 

 (Owen). Ordovician ; Cin- 

 cinnati, Ohio. Natural 

 size. 



Family 1. Oyathaxonidae Milne Edwards and Haime. 



Turbinate or horn-shaped simple coralla. Septa with regular radial arrange- 

 ment. Tabulae and dissepiments absent. Silurian to Permian. 



Cyathaxonia M-ich. (Fig. 102). Acutely pointed, conical. Cardinal septum 

 in fossula. Septa numerous, extending inward as far as the strongly developed 

 styliform and considerably elevated columella. Carboniferous limestone ; 

 Belgium and England. 



VOL. I 



G 



