BRYOZOA. 145 
Pachydictya.] 
This species is closely related to a common form of the Birdseye limestone in 
central Kentucky, which I regard as likely to prove identical with Hall’s Stictopora 
labyrinthica, described from the some horizon in New York. But in the absence of 
any knowledge of the interior of that species, it would be highly injudicious, surely 
unwarranted, to assert their identity. Still, it is possible that even the Minnesota 
form may be only a local variety of that species. However, the probability of that 
Supposition is so remote that I feel no hesitation in proposing the new name varia 
for the form here described. 
Formation and locality.—Restricted to the middle third of the Trenton shales at Minneapolis, Min- 
nesota. A single example from about the same horizon at Cannon Falls. 
Mus. Req. No. 5953. 
Genus PACHYDICTYA, Ulrich. 
Pachydictya ULRICH, 1882, Jour. Cin. Soc. Nat. Hist., vol. v, p. 152; ForRsTE, 1887, Bull. Sci. Lab. 
Denison Univ., vol. ii, pt. ii, p. 162; Mi~LEr, 1889, N. Amer. Geol. and 
Pal., p, 313; ULRicu, 1890, Geol. Surv. Tll., vol. viii, p. 390. 
This genus, in its fullest sense, falls into three distinguishable, yet not entirely 
natural sections, having precisely the same relations to each other as Rhinidictya 
and Hurydictya, Cystodictya, Dichotrypa and Prismopora. These genera, being based 
entirely upon zoarial deviations, are evident to the unassisted eye, and the micro- 
scope is not necessary in distinguishing them. To be consequent, a similar splitting 
up of Pachydictya is suggested, but such a course would be only too liable to lead to 
misunderstandings, since we would be obliged, for the same reason, to follow the 
plan to its logical conclusion in dealing with Ptilodictya and Phenopora, in which 
precisely the same divisions, as well as others equally marked, obtain. It is, there- 
fore, deemed sufficient for present needs to designate two of them with the non- 
committal terms of Section a and Section b. The third, however, being a departure 
in a more obvious and seemingly more important direction, is entitled to better 
attention. For it the name Tricgonopicrya is proposed. 
The following diagnosis embraces the characters of the two sections, but those 
features that may be considered as especially characteristic of one or the other, are 
indicated by the letter a or 6 in parentheses following the statements. 
Zoaria bifoliate, consisting of irregular wide branches, large or small, and more 
or less undulating, leaf-like expansions (a), or of narrow, subparallel-margined. and 
dichotomously branching stipes (4). Margins acute, with a non-poriferous border, 
obliquely striate or grano-striate. Surface with small maculae and, about them or 
taking their places, clusters of zocecia of more or less obviously larger size than the 
average ; occasionally montiferous (a). In other cases (b) these clusters are repre- 
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