. American Paleozoic Bryozoa. as hy! 261 
Specimens of this species vary considerably in the elevation of the 
monticules, some being nearly smooth, while others are strongly tuber- 
culated. Age also makes a difference in the superficial appearance of 
the cells, the peristomes being thinner, and the interstitial spaces 
deeper, in young examples. 
Formation and locality: Niagara group. In the shales of the 
eroup at Lockport, N. Y. The species apparently does not occur at 
any western locality. 
TREMATOPORA HALLI, n. sp. (PI. XIII, figs. 3, 3a). 
Zoarium ramose, slender, branches with an average diameter of 
about .08 of an inch, dividing dichotomously at intervals of one half 
inch, more or less. True zowcia comparatively large, with broadly 
elliptical apertures, and a faintly elevated peristome. On account of 
the variable width of the interstitial spaces, they have not always the 
regular arrangement shown in the figure. At unequal intervals the 
branches present portions on which the cell-apertures are larger and 
more widely separated from each other than ordinary. The longer 
diameter of the apertures varies from ;4;th to ,,th of an inch, while, 
vertically, from seven to nine may be counted in the space of .1 inch. 
Interstitial cells, large and numerous, but usually covered by an inter- 
stitial membrane. A few small spiniform tubuli may be observed in 
well preserved examples. 
In tangential sections the true zocecia are seen to be elongate, sub- 
angular, comparatively thin-walled, and more or less in contact, the 
intervening spaces being occupied by the unequal interstitial cells. 
The spiniform tubuli are small, and easily overlooked. 
Longitudinal sections show that the tubes in the axial region are 
narrow, nearly vertical, and totally without diaphragms. As they near 
the surface they bend abruptly outward, and in passing into and 
through the narrow peripheral region, their diameter is considerably 
increased, and their walls very slightly thickened. The interstitial 
tubes, which are developed just as the true zocecia turn outward, expand 
very rapidly, and have the same beaded character noticed in describing 
T. tuberculosa. The diaphragms too occur at about the same inter- 
vals. (See 7. tuberculosa, Pl. XIII, fig. 25.) 
This species differs from the other small branching species of the 
Niagara group, in its comparatively large, elliptical cells. 
The specific name is given in honor of the accomplished paleon- 
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