BRYOZOA. 163 
Ptilodictya.] ; 
moved, for in that case we would have one easily recognized though not peculiar 
character running through the family that is not represented in Stictoporella and 
allied genera.* A basal articulation, namely, pertains to Ptilodictya, E’'scharopora, 
Phenopora, Clathropora, Graptodictya, and Arthropora, while in Stictoporella and 
genera of that type, the zoarium is continuous throughout, and attached below in 
the ordinary manner, 7. e. by a simple basal expansion forming one piece with the 
erect frond. 
If removed from the Ptilodictyonide it would be necessary to establish a new family 
for their reception, since they cannot, because of the absence of median tubuli 
between their mesial laminz, be placed with the Rhinidictyonide, the only remain- 
ing family of paleozoic Bryozoa with which they have any affinity. It was because 
they agree in this and most other respects with Escharopora, that I arranged them 
with the more typical Ptilodictyonide. The new family would hold an intermediate 
position between the Rhinidictyonide and Ptilodictyonide, differing from the former 
in its zocecial characters, and from the latter in its continuous zoarium, presumably 
a zoarial modification.+ 
Genus PTILODICTYA, Lonsdale. 
Flustra (part.), GOLDFuss, 1826. Petref. Germ. 
Ptilodictya, LONSDALE, 1839, Murch. Sil. Syst., p. 676. 
Ptilodictya (part.), NICHOLSON, 1874. Geol. Mag., n. s., vol. i, p. 128, and Pal. Ont., p. 97; VINE, 1881 
Second Brit. Assoc. Rep. Foss. Poly., Quar. Jour. Geol. Soc. Feb. 1882, 
and 1884, Fourth Brit. Assoc. Rep. Foss. Pol., p. 87; ULRICH, 1882, 
Jour. Cin. Soc. Nat. Hist., vol. v, p. 151, and 1890, Geol. Surv. Ill., 
vol. viii, p. 390; HALL, 1887, Pal. N. Y., vol. vi, p. 19. 
* Escharopora, HALL, 1874 and 1879. Twenty-sixth and Thirty-second Rep. N. Y. State Mus. Nat. 
Hist. (Not 1847, Pal. N. Y., vol. i.) 
Heterdictya, NICHOLSON, 1875. Geol. Mag., and Pal. Ont., (ii) p. 79. 
In my preliminary report on the Bryozoa of Minnesota (Fourteenth Ann. Rep. 
Geol. Nat. Hist. Surv. Minn., p, 64; 1886) I mention the two sections into which 
Ptilodictya, as understood by me in 1882 (Joc. cit.), may be divided. Since then I have 
given the subject further study, with the result that I now believe they may be dis- 
tinguished in a generic sense. 
*An articulated zoarium is of rather common occurrence among both the living and extinct Bryozoa. Of Paleozoic 
types the Arthrostylidw and true Ptilodictyonid@ are the best representatives of this method of growth. It is also character- 
istic of Acrogenia, Hall, and Dicranopora, Ulrich. 
+In drawing this distinction the systematist is once more called upon to decide between zoarial and zowcial varia- 
tions as furnishing the best and most reliable tests of relationship. The more I study these questions of relationship, the 
less practical seems the adoption of strict rules for our guidance in the delimitation of the classificatory sections whereby 
we attempt to express our ideas of natural modifications. What may appear as, and probably is, sufficient ground for the 
erection of a genus or family in one case, does not necessarily suffice in another. There are so many points to be taken into 
account before anything even approximately expressing nature’s handiwork can result. Among them, environment, asso- 
ciation. and relative position in the geological scale, are of great importance. The last, if judiciously used, is always an 
excellent clue to relationship, and one that has been but too rarely taken into consideration by students of recent zoology. 
Volumes are to be written upon these intricate questioas, but I have said enough probably to show that a successful classi- 
fication cannot be worked out in a day, nor is any yet drawn up that will not suffer greater or less modification in time. The 
stability of a classification depends not a little upon the collector, since it is his discoveries that build it up or tear it down. 
