American Palaeozoic Bryozoa. 



243 



structure, and is crossed by the connecting foramina, of which my 

 sections show three or four to enter each tube. The spiniform tubuli 

 are numerous, of moderate size, and have the usual appearance. In 

 longitudinal or vertical sections (Plate X., fig. 7c) the tubes in the axial 

 region have excessively thin, and slightlj' flexuous walls, and are 

 crossed by diaphragms at distances apart of from one to two tube- 

 diameters. As they bend outward into the peripheral region, their 

 walls are much thickened, the diaphragms occur at shorter intervals 

 (one third to one half a tube-diameter), and correspondingly crowded 

 series of cystoid diaphragms are developed in nearly all the tubes. 

 Lastly, the spiniform tubuli may be recognized. 



In transverse sections (Plate X., fig. lb) the tubes are polygonal, the 

 walls excessively thin, and the calcite filling them is divided by irregu- 

 lar cruciform lines, that often are so distinct as to cause the observer 

 some trouble to exactly determine the outlines of the tube walls. (The 

 same feature occurs in many other species of the Monticuliporidce.) 



Formation and locality: Cincinnati Group. An abundant species 

 on the hills surrounding the city of Cincinnati, but very limited in 

 range, being apparently restricted to a few feet of strata at the 300 ft. 

 level. A very similar if not identical form occurs near the top of the 

 formation. 



Homotrypa obliqua, n. sp. (Plate X., figs. 6 and 66.) 



Zoarium ramose, branches cylindrical or compressed, from two to 

 four tenths of an inch in thickness. Typically the surface is covered 

 by rather prominent and closel}' arranged monticules, the summits of 

 which carry cells with thicker walls than the average. The monticules 

 are not a constant feature in this species, examples with an almost en- 

 tirely smooth surface being of frequent occurrence. The ordinary 

 cells are polygonal, have rather thin walls, more or less oblique aper- 

 tures, and a diameter varying from YTo tn to TTo tn °f an inch-. In the 

 axial region the tubes are thin -walled, polygonal, subequal, without 

 diaphragms, and almost vertical in direction, as they pass into the 

 peripheral region, bending outward very gradually, their walls become 

 thickened, and a moderate number of both straight and C} T stoid dia- 

 phragms are developed. The tubes appear to be of one kind only. 

 Tangential sections show, often in a very distinct manner, the con- 

 necting foramina, and a structure of the tube walls precisely similar 

 to that of H. curvata. The spiniform tubuli are small, and more 



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