20 TJic American Geologist. July, i898 
and that the so-called septa are onl\' incomplete new parti- 
tions, because their number is not ahvaj's four; their form 
agrees with that of the projections of ChcBtetes; and because 
the corallites often exhibit long and irregular transversal sect- 
ions, instead of quadratic ones. "A sure decision on the re- 
lationship between C/icstetes and Tetradiuml^' writes Neumayr, 
"depends principally upon the demonstration of the character 
of the walls; if the latter are simple, the differences are so 
small that both genera must be placed into the same family; 
if the walls are double, Tetradiiim can be retained in a sepa- 
rate family, which, however, must be placed directl)' besides 
the Chcstetid<s." 
Lately Dr. F. W. Sardeson* has also expressed his be- 
lief, that the "pseudosepta" of Tetradiiun are onl)- fissional 
partitions. 
The opportunity to study the still doubtful character of 
the "septa" and of the walls, as well as the observation of 
the mode of formation of the peculiar chain-like arrange- 
ment of the corallites, have induced the writer to submit the 
present paper. The investigation was made b\' successiveU' 
grinding off the coralla and by making successive sections of 
especially interesting stages. The figures are all taken from 
sections. 
The youngest stage which could be obtained is represen- 
ted in figure i. The diameter of the corallite is .7 mm. It.s 
most remarkable features are: 
1) The very thick walls which strongl)- contrast with 
the thin walls of later stages. 
2) The complete lack of structure in the walls, which 
are composed of perfectly transparent calcite crystals, while 
the matrix consists of an opaque, fine grained calcareous 
matter. 
3) The distinct formation of the laminae by a plication 
of the entire wall. 
4) The formation of the first two plications in two adja- 
cent quadrants, giving the corallites a symmetrical appear- 
ance instead of a regular one. As the irregular course and 
smallness of the young corallites makes it extremely diflfi- 
*Ueber die Beziehungen der fossilen Tabulaten zu den Alcyonarien 
Stuttgart, i8g6, p. 346. 
