154 THE PALEONTOLOGY OF MINNESOTA. 
[Pachydictya. 
PACHYDICTYA ELEGANS. 2. Sp. 
PLATE VIII, FIGS. 18 and 19. PLATE IX, FIGS. 8 and 9. 
The nearly complete type specimen began its growth on the extremity of some 
undetermined ramose bryozoan. The basal expansion is small, and its surface 
largely covered with granulose striz. At its edges, where it grew downward on the 
foreign body, a few apparently normal zocecia were developed. From the exceed- 
ingly short, neck-like constriction above the base, the erect portion of the zoarium 
divides at once into three branches, and two of these continue to divide dichoto- 
mously with extraordinary frequency, the average distance between bifurcations 
being only 50r6 mm. This frequent division caused the zoarium to spread with 
unusual rapidity ; some of the inner branches must have overlapped if continued. 
We may assume, however, that with age, beyond that shown in this example, the 
outer or subsequent divisions became less frequent, or at any rate, dependent upon 
the space available for lateral development. Branches 2.5 mm. to 5.0 mm. wide, 
thin, edges sharp, non-poriferous, border wide, obliquely grano-striate. In the 
thickest specimens the celluliferous portion of the branch rises abruptly from the 
wide non-poriferous borders, the growth of the latter having failed to keep pace 
with that of the zocecia. Under a good hand lens the surface presents a highly 
ornamental appearance, the arrangement of the zocecia and sculpture of the 
interspaces being very regular. Apertures elliptical, separated from each other 
by spaces as wide as their shorter or transverse diameter. In the central rows - 
the arrangement is alternate, with thirteen or fourteen in 5 mm., measuring 
lengthwise, and seven of the central rows in 2 mm., transversely. Those in the 
marginal rows slightly oblique, a little larger than the average and separated 
by correspondingly wider interspaces, so that a smaller number occurs here in a 
given space than in the central series. Surrounding each aperture a sharply defined 
rim or peristome, and rising from the center of the depressed spaces between the 
longitudinal rows, a faintly flexuous, thread-like line. On the best preserved por- 
tions of the surface, both the longitudinal lines and the peristomes are seen to carry 
a row of minute papilla. Over the central part of the surface the depressed end 
spaces are narrow and usually empty, but toward the margins, where they are 
wider, they are occupied by a gradually increasing uumber of papilla, at first 
isolated, then forming short outwardly tending rows. 
Provisionally I propose to place here a number of specimens agreeing in all 
respects with the type ofthe species, save in this, that they bifurcate at less frequent 
intervals. The interspaces in many are a trifle thicker, but as these specimens are 
heavier and evidently older, that is to be expected. 
