246 



Cincinnati Society of Natural History. 



striated epitheca ; the upper surface convex, and covered by the cell- 

 apertuies. Cells of two principal kinds, large and small, the latter 

 being nearly equally distributed throughout the zoarium. The larger 

 or proper cells have subcircular apertures, arranged in series from six 

 to seven in the space of.l inch. At regular intervals there are scarcely 

 perceptible clusters composed of slightly larger cells. The interstitial 

 cells usually occup} 7 only the spaces left between the points at which 

 the roiuded larger cells are in contact. 



In transverse sections (Plate XI., figs. 2a, and 26) taken just below 

 the surface, the larger cells are subcircular, and in contact at limited 

 points, while each has its own complete, but very thin wall. The an- 

 gular spaces left, which often are rhomboidal, but more frequently of 

 an hour-glass shape, are partially occupied by the interstitial tubes, 

 each of which also has its own distinct wall, and a more or less rounded 

 visceral cavity. The small spaces now left areusuall}' triangular, and 

 filled (apparentl}') by a light-colored, structureless sclerenchyma. In 

 sections taken at a lower level, the appearances presented are somewhat 

 different. The duplex character of the walls is much obscured, if not 

 obliterated, all the cells are more angular, and the interstitial cells are 

 proportionallj' much larger, and usuall} 7 hexagonal. 



Longitudinal sections (PI. XI., fig. 2c) show that the larger tubes 

 are crossed by numerous horizontal, or slightly oblique diaphragms, 

 about two thirds of a tube-diameter apart. The interstitial tubes are 

 likewise crossed by horizontal diaphragms, which are nearly twice as 

 numerous as those in the larger tubes. 



The species above defined has all the essential characters of Nichol- 

 son's genus Diplotrypa. It differs from the previously described 

 species (Z>. petropolitana, Pander, sp., and D. whiteavesi, Nicholson), 

 in having thicker, and more distinctly duplex walls, and less 

 distinctly angular cells. Associated with D. milleri, is a small 

 species of Monotrypa, which so closely resembles it in its growth 

 and general appearance, that, when the specimens are but slightly 

 worn, it is almost impossible to distinguish them without the aid of 

 sections When in a good state of preservation, the thin-walled 

 cells, and the angular cell-apertures which characterize the Monotrypa 

 sp., will serve to distinguish them. 



Named in honor of Mr. S. A. Miller, whose published works have 

 aided so materially to the advancement of the science of pahneontolog}'. 



According to Dybowski, Diplotrypa is a synon3'm for Dianulites, 

 Eichwald. Whether this is true or not, I am unable to sa}v What I 



