BRYOZOA. 379 



i-ella. It is difficult to place D. dubia Ulr., and one or two other 

 species, yet I am satisfied that they are not really congeneric with 

 D. petropolitana. 



BATOSTOMA Ulrich. Irregularly ramose, with a large basal 

 expansion. Zooecia with thin irregularly flexuous walls in the 

 axial region, more or less thickened in the peripheral. Typic- 

 ally the walls are irregularly ovate and ring-like, with those of 

 neighboring cells in contact only at limited points; the meso- 

 pores numerous, irregular in shape and size, and the acantho- 

 pores abundant and with a larger central cavity than usual. 

 Species vary from these to forms with polygonal, thin-walled 

 zoopcia and very few mesopores and acanthopores. Diaphragms 

 strong, horizontal, incomplete in several species. 



Type: B. implicatum Nicholson. Range, Trenton to Cin- 

 cinnati. 



MOXOTRYPA Nicholson, (Ptychonema Hall). Zoaria irregular- 

 ly massive, discoid or subglobose, not divisible into mature and 

 immature regions. Zooecia comparatively large, prismatic, with 

 walls very thin throughout and often undulating or wrinkled 

 transversely; diaphragms remote. Both mesopores and acan- 

 thopores missing. 



Type: M. undulata Nicholson. Range, Trenton to Lower 

 Helderberg, perhaps also in Devonian and Carboniferous de- 

 posits. 



Family CERAMOPORIDJE Ulrich. 



Zoaria usually incrusting, at other times discoid, lamellate, 

 massive, or forming more or less regular hollow branches; 

 rarely bifoliate. Zooecia with lunarium, the apertures usually 

 oblique, of subtri angular, ovate, or, more rarely, polygonal 

 form. The lunarium generally appearing at the surface as a 

 prominent over-arching hood. In forms with direct apertures 

 it appears as a slightlj- elevated portion of the margin, of cre- 

 scentic form, with the ends projecting more or less into the 

 apertures. Mesopores usually present, sometimes abundant, 

 always irregular and without diaphragms. In the zocecial tubes 



