BRYOZOA. 273 
Var, multipora.] 
the rank of a species. Variety multipora, however, though often very distinct (com- 
pare figs. 43 and 45, plate XXIID), is too intimately connected with the typical form 
of the species to admit of greater than varietal distinction. 
My reasons for employing the adopted classifcation instead of the one just 
suggested, and which I really believe to be the best, are dominated by the fact that 
very similar variations are encountered in large collections of D. ulrichi Nicholson, 
sp., an exceedingly common species at Cincinnati, Ohio. This fact makes it, I think, 
not only desirable but necessary that these Minnesota lower Trenton forms be 
studied in connection with the various Cincinnati types of the genus. The most 
important point to be determined by such a study relates to the origin of the Cin- 
cinnati varieties mentioned as being similar to those here separated from prenuntia. 
Did the two sets of varieties have a separate origin, or did those above defined con- 
tinue and develope into the supposed varieties of D. ulrichi? Although these ques- 
tions, whose final solution would require months of careful labor, cannot now be 
answered definitely, sufficient data have accumulated incidentally to render it more 
than probable that a separate origin for the two sets is more nearly the truth of the 
matter. In other words, | believe that future investigation will prove that D. ulrichi 
was developed from some descendant of D. prenuntia, that the known varities of the 
latter became extinct before the close of the Trenton, and that in the Utica and 
Hudson river eras a new set of forms was developed from the D. ulrichi stock.* 
Comparing D. prenuntia and D. ulrichi it is evident that the two species are 
closely related. In the tabulation of the zocecial tubes, which is the least variable 
character in both, they are almost identical. The acanthopores furnish the only 
reliable point of difference, these structures being much more abundant in D. ulrichi. 
Formation and locality.—The typical form and var. multipora are common in the middle third of the 
Trenton shales at St. Paul, Minneapolis, and localities in Goodhue and Fillmore counties. Var. simplex 
occurs in the lower and middle thirds at St. Paul and Minneapolis, while var. nevigera is as yet known 
only from Fillmore county, where it was found in the lower third of the shales. The var. echinata is rare 
in the upper part of the middle third of the Trenton shales at Minneapolis, but abundant in the lower 
part of the upper third at St. Paul, and near Fountain, Minnesota. 
*Tt may be well to add that the var. echinata will probably prove to be the stock that produced Heterotrypa on the 
one side and true Dekayia on the other. Also that the small Dekayella obscura of the Cincinnati rocks may be a degen- 
erate descendant of the var. multipora. 
ailts) 
