American Palaeozoic Bryozoa. 



239 



the summits of which usually appear to be solid, as they are occupied 

 by minute cells; while on their slopes they carry the apertures of 

 slightly larger cells than the average. The largest of these have a 

 diameter of g^th of an inch. The spaces between the* monticules are 

 flat, and are occupied by the polygonal, and moderately thin-walled, 

 ordinary cells, their diameter varying from yy-g-th to y-J-Q-th of an inch. 

 Interstitial cells (if they can be so called) are developed only in the 

 monticules, the summits of which are usually occupied by their 

 apertures. 



Tangential sections (Plate X., fig. 3a) show the tubes to be poly- 

 gonal and thin-walled. Their angles of junction are usually thickened, 

 and the small space thus formed incloses, almost invariably, a minute 

 lucid spot. They represent in all probability very small spiniform 

 tubuli. The appearance of the best section examined leaves me little 

 room to doubt that the tube walls were really pierced b}- uumerous and 

 excessively minute foramina. Where these are not clearly shown, the 

 wall has a peculiar granular appearance. Within the visceral chamber 

 of each of the ordinary cells, the intersected cystoid diaphragms are 

 shown. In a large number the cut edges of the cystoid diaphragm 

 gives the appearance of a secondary oval cell, within the polygonal 

 walls of the tubes. Between the groups of slightly larger cells, a few 

 thick- walled, minute tubes (interstitial) may generally be observed. 



Longitudinal sections (Plate X., fig. 3) show that all the matured 

 tubes have one or both sides lined by a series of cystoid diaphragms, 

 while the space between the double series, or single series and opposite 

 wall, is crossed b}' straight diaphragms, which are placed at distances 

 apart of about one third of a tube-diameter. 



I know of no associated species with which 31. parasitica might 

 for a moment be confounded. It is probably more nearly allied to the 

 M. cincinnatiensis, Nicholson, than to any other species described 

 from the Cincinnati Group. Tne larger, more closely arranged, and 

 much more prominent monticules of that species, constitute a point 

 of difference so decided and readily apparent, that examples of the two 

 species may be distinguished at a glance. 



Formation and localit} r : Cincinnati Group. Not uncommon at 

 Oxford, 0., and other localities, exposing strata having a height 

 equivalent to an horizon of nearly 700 feet above low-water mark in 

 the Ohio river, at Cincinnati, O. 



Moxticulipora wetherbyi, n. sp. (Plate X., figs. 4 46.) 

 Zoarium forming a patch over foreign bodies, to which it is parasi- 



