American Palceozoic Bryozoa. 



167 



The wide segments, thick cell-walls, and remarkably short articu- 

 lating branchlets constitute the distinguishing features of the species. 



Formation and locality: From the upper part of the Cincinnati 

 group, near Oxford, Butler county, Ohio. 



Dicranopora trentonensis, u. sp. (Plate VI., figs. 15, 15a.) 



A segment of this species gave the following measurements: from 

 the point of bifurcation to the extremity of the simple end, .7 inch; 

 from do. to the upper or articulating end of each of the two branches, 

 .3 inch; width of main stem, the sides or edges of which are nearly 

 parallel, .08 inch; width of branches, .07 inch; angle of bifurcation, 

 about 80 degrees. The cells are arranged between slightly raised 

 longitudinal lines; there are nine of these rows, besides one obliquely 

 directed series along each edge; measured longitudinally, seven cell- 

 apertures occupy the space of .1 inch. Cell-walls comparatively thin 

 Non-poriferous margin distinct but narrow. 



The thin cell-walls and long branches of the segments are the dis- 

 tinguishing characters. So far as the length of the two branches is 

 concerned, the extremes noticed are shown in this and the preceding 

 species. 



Formation and locality: From the middle Trenton strata, exposed 

 at Lebanon, Tenn. 



Arthropora, nov. gen. 



Growth of Zoarium similar to that of Dicranopora, but not so 

 regular. Each segment has several short spurs or branchlets proceed- 

 ing from each edge, some of which may or may not be tipped for 

 articulation with succeeding segments. The main stem however is 

 always slightly thickened and solidified at each end, where it joins the 

 preceding and succeeding segments. The cell-mouths are oval or 

 circular, and separated by interstitial pits or sulci. Often the cells 

 are closed by sculptured opercula. 



Type, Stictopora shafferi, Meek. (Plate VII., figs. 10 and 10a.) 



Meek's description of this species is in the main correct, but he 

 did not notice that the zoarium is a jointed one. I have in my cabinet 

 a specimen which preserves no less than forty of the segments in 

 connection. Figure 10, on plate VII., represents four of the segments 

 of that specimen, and gives a tolerably clear idea of the growth of the 

 zoarium. Besides Arthropora shafferi, the Cincinnati group furnishes 

 at least one, and probably two other species, having the characters 

 above ascribed to the genus. 



