23 
All that is intended here is to point out how it differs from the coenenchyme 
of such forms as Plasmoporella (Kiaer 1899, 34-36, Taf. V, 9 and 11, and 
1929, Plate V, figures 6, 7), Propora, and Heliolites. In the latter case, of 
course, the situation is widely different because of the presence of siphono- 
pores. In the former two the secreting base outside the corallites has lost 
its primitive polypal character and functions as a common layer, secreting 
a vesicular and true coenenchyme (Plate III, figures 4a-b), 
The effect of this variation in Calapoecia is a separation of those parts 
of the corallites contained within the stereozone. When it is compared with 
the astraeoid trend (Lang 1923, 123) it becomes apparent at once that the 
two are analagous and certainly not homologous. As seen in the Rugosa 
(Ogilvie 1896, Smith 1916, 281-3) the astraeoid trend effects the isolation 
of the tabularia of corallites by the. formation of a common substance 
between them. But this common substance is produced from the dissepi- 
ment zones of neighbouring corallites. Now in Calapoecia there is no zone 
of dissepiments. In reconstructing the method by which the coenenchyme 
is produced it is essential to think of the corallites in the typical C. 
canadensis state as growing apart one from another to give the interspaces 
that are occupied by the structures laid down by the extra-stereozonal 
portion of the corallites. Until such interspaces are produced there will, of 
course, be no room for the development of “ cost® ” and the tabula-like 
plates of the coenenchyme. In the performance of the astraeoid trend the 
inter-tabularia zones are, so to speak, ready-made, in that the dissepimental 
tissue already exists in the corallites; but in Calapoecia the coenenchyme 
cannot be developed until room is made for it by the divergence of the 
corallites. Thus the stereozone in the typical C. canadensis and that of 
var. anticostiensis remain with roughly the same diameter; whereas in the 
Rugosa, before the astraeiod trend can be effected, the zone of dissepiments 
must have originally encroached upon the tabularium, thus reducing the 
diameter of that area which we may compare with that within the stereo- 
zone in Calapoecia. 
RELATIONSHIPS OF CALAPOECIA 
The conclusion of the variation already studied in Calapoecia can, 
perhaps, be traced out in specimens regarded as Sarcinula organum (Linn.). 
The writer is indebted to Dr. Stanley Smith for making clear the 
synonymy of this form. With no wish to anticipate their publication, 
he proposes briefly to indicate the conclusions reached by Drs. Lang and 
Smith on this point. Sarcinula perforata Lamarck and Madrepora organum 
Linnaeus (1758) are the genosyntypes of Lamarck’s genus Sarcinula (1816, 
222). The name was irrevocably attached to Madrepora organum Linn, 
by Dana in 1848, where it is cited as the type of Lamarck’s genus. The 
Spring ophyllum of Edwards and Haime (1850-4) is monotypic with 
Sarcinula Lamarck Dana and thus is a nomen nudum. M’Coy (in label- 
ling specimens) and other authors have followed Edwards and Haime’s 
error, consequently their Spring ophy Hum organum is a synonym of Sar- 
cinula organum, as employed below. The writer has searched for the type 
