BRYOZOA—CRYPTOSTOMATA. 147 



tion on opposite sides of each weaker longitudinal bar. The 

 underlying branches have each a low carina with circular pores 

 with peristomes, on either side, and are connected by depressed 

 dissepiments half as wide as the branches. 



Keokuk of Illinois and Iowa ; Warsaw of Illinois and Missouri ; 

 St. Louis of Kentucky. 



LVI. Reteporidra Nickles and Bassler. 



Flabellate or undulating expansion with thickened margins, the 

 sinuous or zigzag non-carinate branches anastomosing at short 

 and regular intervals, producing a regular series of oval fenestrules ; 

 apertures in three to seven rows, non-celluliferous side not striated. 



97. R. perundata (Hall). (Fig. 201, h.) Mid-Devonic. 

 Fenestrules oval, irregular, non-celluliferous face angular or 



carinated, celluliferous rounded ; cell apertures in from three to 

 five ranges. 



Hamilton of Western New York, etc. 



LVI I. Archimedes Owen. 



Like Fenestella, but spirally wound and supported by a solid 

 calcareous central axis, which is often the only part remaining 

 intact. 



98. A. communis Ulrich. (Fig. 205, b r .) Mississippian. 

 Central axis or "screw" long, slender (1 to 2 mm. in diameter) 



and uniformly coiled, 7 or 8 volutions in 20 mm., the fenestrated 

 portion forming an angle of from 85 to 90 degrees with axis. {A. 

 intermedins Ulrich makes an angle of 72 degrees and has some- 

 what fewer whorls. A. swallozvanus varies from 2.8 to 6.J mm. 

 in diameter, and has an average of 5 volutions to 20 mm., the 

 angle of divergence of the fenestrated portion being 85 degrees. 

 A. proutanus Ulrich has from 5 to 7 volutions in 20 mm., and an 

 angle of 65 degrees for the fenestrated part. It is somewhat 

 thinner than A. communis.} 



Chester of Kentucky and Illinois. 



99. A. wortheni (Hall). (Fig. 205, a.) Mississippian. 

 Screw large and coarse (5 to 10 mm. in diameter), volutions 



either right- or left-handed, from 5 to 6 in 50 mm., fenestrated 

 portion diverging at an angle of about 65 degrees. Zooecia 

 separated by strong spinose carina. 

 Warsaw of Illinois. 



