NORTH AMERICAN EARLY TERTIARY BRYOZOA. 



323 



Affinities. The elements' of the olocyst (fig. 20) are regularly disposed in 

 quincunx. 



~i x 14 

 R -,?n 

 A X20 



FIG. 91. Genus Pachytheca Canu, 1913. 



A, B. Pachytheca filiformis D'Orbigny, 1852. A. Zoarium, X 20. B. Longitudinal section, 

 X 20. (A, B after Canu, 1913.) a, ascopore; ap, apertura ; /, frontal thickening; p, peristomie; 

 pis, peristomice; z, zooecium. 



C, D. Pachytheca bosqueti Beissel, 1863. C. Cast of the interior, X 35. D. Extremity of a 

 branch, profile view, X 14. E. The same extremity seen from the top, X 14. (CF after 

 Beissel, 1S63.) 



This species differs from Beisselina midwayanica in its very large frontal pores, 

 in the somewhat larger diameter of the peristomice (0.09 mm. instead of 0.06 mm.), 

 and in its somewhat prominent peristome. 



A '20 



FIG. 92. Genus Beisselina Canu, 1913. 



A, B. Beisselina boryana von Hagenow, 1S51. A. Surface of zoarium, X 20. B. Longitudi- 

 nal section, X 20. (A, B after Canu, 1913.) a, ascopore; ap, aperture; av, avicularian cavky: 

 /. frontal thickening ; ov, ovicell ; p, peristomie ; pis, peristomice ; z, zooecium. 



C Beisselina striata Goldfuss, 1S27. Longitudinal section, X 20. Lettering same as 

 on fig. B. 



Occurrence. Midwayan (Clayton limestone) : Mabelvale. near Little Kock. 

 Arkansas (rare). 



Cotypes.C&t. No. 63820, U.S.N.M. 



