NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
323 
Affinities . — The elements of the olocyst (fig. 20) are regularly disposed in 
quincunx. 
Fig. 91. — Genus Pachytlieca Canu, 1913. 
A, B. Pachytlieca 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. (C-F after 
Beissel, 1863.) 
This species differs from Beisselina midway anica 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. 
Fig. 92. — Genus Beisselina Canu, 1913. 
A, B. Beisselina boryana von Hagenow, 1851. A. Surface of zoarium, X 20. B. Longitudi- 
nal section, X 20. (A, B after Canu, 1913.) a, ascopore; ap, aperture; av, avicularian cavity; 
f, frontal thickening ; ov, ovicell ; p, peristomie ; pis, peristomice ; z, zooecium. 
C Beisselina striata Goldfuss, 1827. Longitudinal section, X 20. Lettering same as 
on fig. B. 
Occurrence . — Midwayan (Clayton limestone) : Mabelvale. near Little Rock. 
Arkansas (rare). 
Cotypes. — Cat. No. 63820, U.S.N.M. 
