BRTOZOA. 623 







PTILOPORA VALIDA Ulrich. 



PL LXV. fijfs. 5-5-, PL LXVI, figs. 1-lb. 



Zoarium a narrow, pinnated frond, the entire width not known 

 to exceed 1.5 cm., often closely resembling a robust Pinuato- 

 pora. 



Eevei-se. Midrib comparatively strong, convex, 0.7 to 1.3 

 mm. wide, and like the branches finely striated longitudinally. 

 Branches comparatively short, rather rigid, 0.4 to 0.5 mm. 

 wide, given off from the midrib at an angle of about 55, 

 averaging ten on each side in 1 cm. At long intervals one of 

 the branches grows stronger than the rest, and forms a new 

 midrib, with branches like the primary one. Dissepiments de- 

 pressed, thin, generally about 0.2 mm. wide, rarely more than 

 three between any pair of branches. Fenestrules oblong sub- 

 quadrate or oval, with average dimensions of 1.3 by 0.5 mm.; 

 three occupy a space nearly 5 mm. long. 



Obverse. Midrib with a strong rounded carina, carrying small 

 nodes about 2 mm. apart. Branches subcarinate, also with 

 small but more closely arranged nodes. Zocecia in two ranges 

 on both midrib and branches. Apertures rather large, fourteen 

 on the midrib and sixteen on the branches in 5 mm., their 

 diameter or less apart. With age, the midrib thickens and the 

 apertures are covered by a finely striated deposit. Often, too, 

 the branches are broken away, when the fossil presents an ap- 

 pearance that at first sight is quite puzzling and liable to cause 

 mistakes. 



The narrow fronds and thin dissepiments separate this species 

 from P. acuta. 



Position and locality: Keokuk group. Bentonsport and 

 Keokuk, Iowa, and Jersey Co., 111. 



PTELOPORA CYLINDRACEA Ulrich. 



PI. LXVI, fig. 2-2b. 



Zoarium when complete a narrow pinnate frond, with the 

 branches extending about 5 mm. on each side of the midrib. 

 Usually the branches are all broken away so that the zoarium 

 looks like a slender rod with two ranges of small cells, and two 



