Review of Recent GeoUxjical Literature. 39 
subsequent calcareous deposition, into a more or less solid mass; (2) the 
symmetry is invariably by eights, there being eight fringed tentacles 
and eight mesenteries: (3) the polyps do not normally form calcareous 
thecEe and never, as in other corals, form septa developed between the 
mesenteries; (4) the colony is usually dimorphic. 
In the aberrant type Heliopora the skeleton is not made of small club- 
shaped spicules like the other Alcyonaria, but is composed of long 
spicular rods, parallel and in contact, forming a dense stony structure. 
The apparent septa are the result of the so-called coenenchymal gem- 
mation, are not formed between the mesenteries, of which they are 
wholly independent in number and position. They are. therefore, not 
septa but pseudosepta. 
In looking for these typical structures in the forms ranked by Mr. 
Sardeson with the Alcyonaria we find them peculiarly lacking. With 
scarcely an exception the skeletal tissue of these forms is not spicular 
but solid. This difficulty is met by Mr. Sardeson by invoking a great 
principle: "The reduction of an originally compact, calcareous skeleton 
to a spicular one or its transmutation to a horny one, or eventually to a 
disappearance of the skeleton altogether," which has been active among 
"the sponges, coelenterates and many mollusks." It seems, however, 
that this principle cannot be looked on as of universal application, nor 
even as a matter of common occurrence, exceyjt perhaps in diverted and 
isolated types. Therefore, until the relationship between the tabulates 
and the Alcyonaria be proved more satisfactorily than Mr. Sardeson 
has succeeded in doing, we cannot accept this law as applying to this 
particular case. 
That the fossil tabulates nearly always develop septa of some kind, 
is met by calling all the structures referred to, pseudosepta, as those 
of Heliopora. The distinctive character of pseudosepta, however, is 
that they are independent of the polyp in whose calyce they occur. 
They, therefore, are small and indefinite in number. They vary in ma- 
ture individuals of the same colony and in the same individual at dif- 
ferent points in its development. Ntnv, in the fossil tabulates the septa 
are sometimes quite well developed and they are usually constant in 
number. They are probably not pseudosepta then, but true sejjta. 
Indeed, it is interesting to observe the strange recurrence of the cabal- 
istic number twelve in connection with the vertical septal rows; so 
much so, in fact, as to justify the belief long held, that in most of the 
fossil tabulates the symmetry of the polyps was by sixes instead of 
eights. 
As to dimorphism, except in monticiiliporoids, which good authorities 
refer to the Bryozoa, it is conspicuously absent. 
To discuss a particular case, one to which Mr. Sardeson has given 
more personal study, perhajjs, than to any other and which is the first 
one treated in his fjaper, the relationship of Heliopora to Heliolites. 
Heliopora seems to be more closely related to Heliolites, than are any 
other of the Palaeozoic corals discussed, to what the author regards as 
their living representatives. The similarity between these two genera 
has long been recognized, but is, I believe, generally ovi-icstiiiiatetl. 
