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Cincinnati Society of Natural History. 



Rhombopora persimilis, n. sp. (PI. I., figs. 7, 7 a, 7b, 1c, Id.) 



Zoarium ramose, branches cylindrical, rigid, very slender, about .035 

 inch in diameter. The mode of branching is characteristic. The 

 stems do not divide dichotomously, but the branches are thrown off at 

 nearly a right angle from a main stem. The intervals between these 

 branches vary greatly, some specimens remaining undivided for a dis- 

 tance of nearly three fourths of an inch. Zocecia arranged very 

 regularly in vertical, transverse, and more particularly in diagonally 

 intersecting series; apertures elliptical, occupying the bottom of dis- 

 tinct, sloping, rhombic or acutely elliptical vestibules, the margins of 

 which are ornamented by a single row of small spiniform tubuli. A 

 larger spine, though often missing, is usually placed between the ends 

 of the cells. The zooecial apertures are sometimes covered with centrally 

 perforated opercula. Measuring in the direction of the vertical series, 

 about five and one half cells occupy the space of .1 inch; in the trans- 

 verse rows, twelve, and along the oblique series, ten may be counted 

 in the same space. The number of vertical series around a stem 

 varies from twelve to fifteen. 



Tangential sections (PI. I., fig. la) are, on account of the small size 

 of the zoarium, difficult to prepare, but when satisfactory they pre- 

 sent the usual characters belonging to species of this genus. The 

 section figured shows all the peculiarities noticed. 



In longitudinal section (PI. I., 7c) three or four tubes in the axial 

 region are nearly vertical and extremely long, and ma}' be called parent 

 tubes, as the greater number of cells are developed from these by gem- 

 mation. In the peripheral region ; which is comparatively narrow, the 

 walls are abruptly thickened, and the tube cavities constricted by the 

 angular projection of the inferior wall. The spiniform tubuli are 

 easily distinguished. Diaphragms have not been detected, but at the 

 bottom of the vestibule the thin opercular covering of the cell aper- 

 tures may often be detected. 



Transverse sections (PL I., fig. 76) show that the axial region is 

 occupied by numerous thin-walled and unequal polygonal cells. 



In some respects this species is allied to B. lepidodendroidea, but 

 the two are not likely to be confounded. The cells, and branches 

 of that species are larger, and the mode of growth is different, while 

 the direction of the tubes in the axial region of the zoarium is 

 also quite different. It is almost impossible to separate fragments 

 of this species from those of Rhabdomeson gracile, Phill., by their 



