138 THE PALEONTOLOGY OF MINNESOTA. 
([Eurydictya. 
zocecial apertures are to be counted in 5 mm., while twelve rows occur on a branch 
3.0 mm, wide, on which the non-poriferous borders occupy space amply sufficient to 
accommodate another row on each side. 
Internal characters not observed, the process of fossilization having been too 
unfavorable to preserve the minuter details of structure. 
The small footstalk, rapid spreading of the zoarium, and the wide marginal 
space, are the characters relied upon in distinguishing this species. In other respects 
the species is very near RF. trentonensis and R. grandis. 
Formation and locality.—A\l the specimens seen were collected by the author from the lower lime- 
stone of the Trenton formation, at Minneapolis, Minnesota. 
Mus. Reg. No. ?5934. 
Genus EURYDICTYA, Ulrich. 
Eurydictya, ULRICH, 1889. Miller’s N. Amer. Geol. and Pal., p. 301; 1890, Geol. Surv. Tll., vol. viii, 
pp. 389 and 520. 
Zoaria bifoliate, consisting of broad, simple or irregularly divided expansions, 
the surfaces of which exhibit more or less conspicuous, though usually small, macule 
or monticules. Zocecia of the same type as in Rhinidictya. 
Type: E. montifera Ulrich, 1890. Geol, Surv. Il. vol. viii, p. 521. 
This genus was established for the reception of a small group of Lower Silurian 
species that, though intimately related to Rhinidictya, Ulrich, it seemed desirable to 
distinguish from that genus. The broad and undefined zoarial expansion pertaining 
to the several species gives them a very different aspect from that presented by the 
narow, parallel-margined, and regularly branching stipes so strictly adhered to by 
all the true species of Rhinidictya. That intermediate forms occur is true, nor can 
we doubt that the dividing line between the two genera will continually grow more 
shadowy with the discovery of new species. But, as that difficulty is encountered 
by the systematist throughout all organic nature, it cannot be regarded as a bar to 
the formation of generic groups, because, theoretically, if the course were carried to 
its logical conclusion, all necessity for classification would cease. Some recognition 
of obvious departures from a type is necessary, and in the present incompleteness of 
our knowledge the only satisfactory plan to accomplish this is to adhere strictly to 
the binomial nomenclature. In this declaration I am to be understood as aiming at, 
subgeneric rather than varietal designations. 
Eurydictya multipora (2 Hall’s sp.), the only species of the genus so far known to 
occur in Minnesota, is the least typical of the genus. In shape and structure of its 
end walls the species approaches Phyllodictya varia. The type of the genus, H. mon- 
tifera, may be looked for in the upper beds of the Hudson River group in Fillmore and 
other counties in the southern part of Minnesota where that horizon is exposed. 
