SUB-CLASS I ANTHOZOA—TETRACORALLA 73 
without coenenchyma, but with usually strongly developed endothecal tissue in the forin 
of tabulae or dissepiments, and with well-marked, frequently wrinkled wall. 
The Tetracoralla are especially characterised by the possession of four 
principal or primary septa, between which four sets of new septa are subse- 
quently developed. The four principal septa are sometimes of equal propor- 
tions, when they may be either stouter and longer than the others (Stawria), or 
thinner and shorter (Omphyma); or they may be of unequal proportions. Of 
the two principal septa which lie in the longitudinal axis of the corallum, one 
(called the cardinal septum) is frequently s situated in a depression or faon 
known as the fossula (Fig. 104); while the other or cownter septum is either 
normally developed, or is more or less reduced. Occasionally the counter 
septum is placed in a fossula, while the cardinal septum is normally developed : 
but the two laterally disposed or alar septa are always equal in size. The 
remaining septa not infrequently exhibit a well-marked radial arrangement, in 
which the longer and more strongly 
developed usually alternate with the 
shorter and less strongly developed. 
New septa, according to Kunth and 
Dybowski, are inserted in the follow- 
ing order. First, a new septum is 
given off on either side of the cardinal 
septum (Fig. 104, /), 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 | Menophyllwm tenuimar- 


s 3 ginatum, E. and H. Car- . s 
they diverge from the cardinal septum, boniferous Limestone ; Eee Neh 
Tournay, Belgium. 2/). Zaphrentis Canadensis, 
as they grow upward, in a pinnate h, Cardinal septum; 49, Bill. Ordovician; Cin- 
fashion. Likewise the two counter Counter septum; s, Alar cinnati, Ohio. Natural 
quadrants lying between the alar and ane ue 
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 i in the Tetracoralla will be readily understood on inspecting 
the surface of such specimens whose septa are visible on the exterior, or whose 
wall is readily removed by corrosion or polishing. One may then note three 
distinet 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. 105). The order in which the septa 
are given off in the four quadrants is indicated by the numerals in Fig. 104. 
Many of the Tetracoralla multiply by sexual reproduction, and occur only 
as single individuals; asexual reproduction takes place usually by calicinal, 
more rarely by lateral gemmation, and results in dendroid or massive colonies. 
Dissepiments are generally abundantly 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 
