94 Diphyphyllum Sifnco^nse (Bill) Rom.—Sherzer. 
and at distances varying from one to three millimeters, more 
prominent single ridges give character to the external stem. 
By means of a pocket magnifier a third set of very delicate, 
closely approximated wrinkles may be distinctly seen. 
Adult corallites average five or six millimeters in diameter, 
are somewhat loosely and irregularly set, usually less than a 
diameter apart and occasionally coalescing for a short dis- 
-7:=r<S xflSffliiv t^'^ce. The nature of the calyx is 
unknown. The number of septa 
is quite regularly 44 ; alternately 
longer and shorter. The longer are 
somewhat flexuous, as seen in cross 
section, and extend about two- 
thirds of the distance from the outer wall to the center, rarely 
reaching it. The shorter septa extend about one-fourth of this 
distance and are intersected near their centers by a thin but 
very distinct inner wall, at a distance of from .5 to .75 of a 
millimeter from the outer. This second wall is as thick and 
as well defined as the outer, and is separated from it by a single 
row of vesicles, shown in the longitudinal section ; these vesi- 
cles averaging .4 of a millimeter in hight. This arrangement, 
of course, gives no trace of dissepiments in cross section 
except where double vesicles intervene seemingly by accident. 
The inner area is occupied by a series- of laterally depressed 
tabulae ; about fifteen in the space of ten millimeters, termi- 
nating at the inner wall. These are somewhat irregular, but 
nearly horizontal and flat at the center ; sometimes uniting 
with each other before reaching the inner wall. In regard to 
the nature of this second wall there can be no doubt it exists 
in all the stems, distinctly defined; a continuous ^^rixMon 
separating the vesicular from the tabular area. 
In growth, size and in the number of septa this specimen is 
identical with Eridophyllum simcoense Billings, or what Dr. 
Rominger prefers to call Diphyphyllum simcoiinse. In the 
original description of this species Billings makes no mention 
of a second wall, and Rominger asserts that none exists. 
However, in specimens identified by the latter as simcoense 
and now in the museum of the University of Michigan, iden- 
tically the same structure is seen in the best preserved stems, 
and in others traces of the same inner wall frequently occur, 
even in the specimen the photograph of which is given in 
