BRYOZOA. 591 



POLYPORA RETRORSA Ulrich. 

 PI. LIX, flgs. 6-6d. 



Zoarium a small, rapidly expanding, foliar net-work. Branches 

 6.5 to 7 in 5 mm., rounded, slender, averaging 0.4 mm. in 

 width, but increasing from 0.3 to 0.5 or 0.6 mm. before bifurca- 

 tion takes place. Dissepiments short, depressed, half as wide 

 as the branches. Fenestrules long-oval or sub-quadrangular, 

 five or six in 5 mm., narrower than the branches. Zocecia in 

 three or four alternating ranges, in each about twenty in 5 

 mm. Apertures small, sub-oval, seemingly directed backward 

 on account of the peristome, which is much the highest on the 

 anterior side; sometimes with a rayed appearance. On the re- 

 verse the branches and dissepiments are rounded, occupy the 

 same plane, are nearly of the same thickness, and exhibit nu- 

 merous distinct granules, arranged in one or two encircling 

 series. The fenestrules are shorter than on the obverse, and 

 regularly elliptical in form. 



The distinct granules and rounded fenestrules of the reverse, 

 and the unequally developed peristome separate this species 

 from, at any rate all the Carboniferous species of the genus, 

 known to me. 



Position and locality: Keokuk group. Rather rare at Keo- 

 kuk, Iowa. 



POLYPORA RADIALIS Ulrich. 



PI. LX, flgs. l-ld. 



Zoarium very small, compact, two or three cm. in diameter, 

 originally flabellate, but by expanding very rapidly the lateral 

 margins at last meet and unite, giving it the appearance of a 

 very much depressed funnel. Branches comparatively strong, 

 close together, 0.3 to 0.5 mm. wide, and eight or nine in 5 mm., 

 their surface minutely granulose. Dissepiments short, depressed, 

 varying from one-fourth to two-thirds the width of the branches, 

 their width depending largely upon the relative proximity of 

 neighboring branches, being widest when these are nearest. 

 Fenestrules small, irregular, sub-oval, about 0.5 by 0.2 mm., 

 and between six and seven in 5 mm. Zocecia in two ranges im- 



