BRYOZOA. Ul 



Phyllodlotya.l 



then learned to esteem caution, the present less positive stand on the question will 

 suffice till we have been informed of the minute structure of Hall's types. These 

 were derived from the northern part of Wisconsin, and if they prove to be identical 

 with the specimens here described,* a considerable extension of the geographical 

 range of the species will result. The species is an important one too, in being 

 highly characteristic of one horizon. 



, Formation and loeality.— la Minnesota known only from the upper third of the Trenton shales, at 

 St. Paul. In Kentucky, rather jjommon in the shales above the " Modiolopsis beds." In Tennessee it 

 holds the same horizon (Safford's Middle Nashville Series) at Nashville. 



Mus. Reg. No. 5942, 



Genus PHYLLODICTTA, XJlrich. 



Phyllodietya, Uleich, 1882, Jour. Cin. Soc. Nat. Hist., vol. v, p. 153; Miller, 1889, North Amer. 



Geol. and Pal., p. 315 ; Ulrich, 1890, Geol. Surv. 111., vol. viii, p. 390. 



Zoaria bifoliate, simple or iregularly branched, growing from an expanded basal 

 attachment. Zooecial tubes long, with complete diaphragms but no hemisepta ; from 

 the central axis they bend outward very gradually, causing the apertures to be more 

 or less strongly oblique, with the posterior edge raised lip-like. Interspaces wide, 

 subsolid, transversed vertically by one or two rows of minute tubuli, which appear 

 as so many papillae at the surface. 



Type : P. frondosa Ulrich. 



This genus requires more study before the relations to Eurydidya on the one 

 side, and Pachydidya on the other, can be determined and satisfactorily established. 

 The questions involved are rendered difficult of solution by the commingling of 

 characters found in Pachydidya splendens Ulrich. and P. firma Ulrich, of the upper 

 beds of the Hudson River group, and Eurydidya muUipora (?Hall) of the Trenton 

 group. All three of these species have certain features in common that do not per- 

 tain to the more typical forms of either Pachydidya or Eurydidya. It is, however, 

 precisely in those characters that these species remind us of Phyllodidya.* Though 

 having an abundance of specimens of, at any rate the majority of the species, bear- 

 ing directly upon the points at issue, I have been obliged, chiefly because of a lack 

 of time, to defer pushing my investigations to a satisfactory conclusion. I realized 

 also that all partial studies of the group of bifoliate Bryozoa, and consequent rear- 

 rangements of species, are only too likely to prove premature and faulty when the 

 full results of a complete study of the group shall have become available. For the 

 present it is sufficient to point out the obscure and perhaps weak spots in the classi- 

 fication now in use. 



♦Another genus presenting points of agreement with PhyUodictya is Ptilotrypa Ulrich, founded upon a single species 

 from the upper heds of the Hudson River group. But the ahsence of " median tuhuli " in the latter Is a difference of 

 such Importance that the two genera must he regarded as widely distinct and as helonging to different families. 



