American Palceozoic Bryozoa. 249 



though quite distinct, is yet so near to M. cequalis, that despite the in- 

 terstitial tubes, I can not regard it as belonging to another genus. 



Formation and locality: Cincinnati Group. Rather rare at several 

 localities about Cincinnati, O., at an elevation of 100 to 200 feet above 

 low-water mark in the Ohio river. 



MoNOTRYPELLA SUB QUA DR ATA, II. Sp. (Piatt XL, figS. 4-46.) 



Zoarium ramose, the branches slender, cyclindrical, and from one to 

 nearly two tenths of an inch in diameter. Surface smooth, without 

 monticules or clusters of large cells. Cells usually quadrate or rhom- 

 boidal, the apertures circular or broadly elliptical, and arranged in 

 regular, more or less curved diagonal lines; at other times the arrange- 

 ment is peculiar^ irregular. Their walls are moderately thick, and 

 on an average twelve may be counted in the space of .1 inch. A few 

 smaller cells (which sections show to be of the nature of interstitial 

 tubes) are intercalated among the ordinary cells. 



Tangential sections (Plate XL, fig. 4a) show that the tubes have 

 moderately thick walls, which preserve, more or less distinctly, the 

 primitive boundary line between adjoining tubes. Small interstitial 

 tubes are always shown, and although their number varies in different 

 sections, they are never numerous. 



In longitudinal sections (Plate XL, fig. 46) the tubes in the axial 

 region of the branch have very thin walls, and diaphragms are usually 

 wanting in this region. As they approach the surface their walls are 

 moderately thickened, and comparatively remote horizontal diaphragms 

 are developed (from one half to two tube-diameters distant from each 

 other). Occasionally the section cuts one of the interstitial tubes, in 

 which the diaphragms are about nearh'as numerous as in the ordinary 

 tubes. The development of young tubes, by gemmation, takes place 

 simultaneously in all the tubes at a point on a line crossing the branch 

 at regular intervals, with a strong upward curve. Eight or nine of 

 these intervals occur in the space of .3 inch. In transverse sections 

 the tubes in the central portion of the branch are thin-walled and 

 strictly quadrate or rhomboidal. 



In many respects this species closel}' resembles M. quadrata, Rom 

 inger, and might almost be regarded as a dwarfed variety of that 

 species, were it not for the certain presence of interstitial cells 

 in M. subquadrata. Another difference is found in the size of the 

 cells, Rominger's species having from seven to eight in the space of .1 

 inch, while in the new species there are about twelve in the same space. 



