654 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
Generally the zooecia are either cylindrical or pyriform. In many of those forms which 
have cylindrical zooecia throughout the greater part of the zoarium, the zooecia between 
the first and third dichotomies tend to be slightly pyriform ; while in those forms with 
pyriform zooecia, the zooecia between the first and third dichotomies are generally more 
pyriform than the rest. 
Ribbing, when present, is usually faint at its first appearance, becoming stronger later 
on, and in some cases becoming fainter again finally. The point at which the acme is reached 
varies a great deal. 
Finally, Lang has demonstrated that the method of branching and the shape 
of the zooecia varies sensibly in time and according to the successive geologic 
stages (fig. 215A). 
In the application of these observations Lang, in order to characterize a 
species of Stomatopora , made a large table, 1 which is an excellent example of 
bookkeeping. We are unfortunately not able to adopt this method in our work as 
we do not possess a sufficient number of specimens of our various species. 
Before Lang’s studies, Gregory, in 1896, hud also devised a system of descrip- 
tion, which, however, was given up in the succeeding volumes of the Catalogue of 
the British Museum. In order to make the species collected in our American 
Tertiary formations of stratigraphic value we have no other method than that 
of good illustrations always on the same scale (X12 and X25). 
The branches of the same zoarium of Stomatopora or of Proboscina never 
grow over each other (see pi. 105, fig. 1) ; a branch is arrested in growth when it 
encounters another. What is the mysterious force which permits the minute 
branches of the same colony to be cognizant of each other in the eternal night of 
the oceanic depths ? Evidently this is a manifestation of a kind of cerebral activity 
of which the nerve ganglion of the bryozoa is the organ. But how does the trans- 
mission of the sympathetic vibrations occur and by what magic do they become 
synchronized? Although microscopic the biologic mechanism of a zoarium is 
sublime. 
STOMATOPORA OPPOSITA, new species. 
Plate 107, fig. 25. 
Description— The zoarium is not dichotomous; the branches are opposed and 
are emitted symmetrically at the distal extremity of a tube. The tubes are short, 
finely punctate, elliptical. The peristome is orbicular, thick, little salient. 
I Diameter of tube 0.36 mm. 
Measurements. — Length of tube 0.50-0.70 mm. 
Diameter of peristome 0.20 mm. 
Occurrence. — Midwayan (Clayton limestone) : Mabelvale, near Little Rock, 
Arkansas (very rare). 
Tlolotype. — Cat. No. 65247, U.S.N.M. 
1 Lang, Geological Magazine, vol. 2, 1905, p. 262 ; vol. 4, 1907, p. 23, etc. 
