EARLY PALEOZOIC BRYOZOA OP THE BALTIC PEOVIlSrCES. 139 



62 a and c, while the surface characters of the former are shown in 

 figure 62 &. The zoarium grows from a spreading attached space 

 into narrow, bifohate branches with thin, sharp, nonporiferous edges. 

 Wlien magnified the celluhferous side in the very regular arrange- 

 ment of the zooecia and sculpture of the interspaces presents a highly 

 ornamental appearance. The apertures are elliptical and separated 

 from each other by spaces equal to their shorter diameter. Around 

 each aperture is a well-defined peristome, and between the longitudi- 

 nal rows of zooecia a flexuous, thread-like line is developed. These 

 peristomes and longitudinal lines bear a row of minute papillae, wliich 

 increase the ornament of the surface. Five to five and one-half 

 zooecia in 2 mm., measuring lengthmse, and seven rows in 2 mm., 

 coimting transversely. 



Fig. 62.— Pachydictya elegans. a, neaely complete zoarium, natural size, branching more 



FREQUENTLY THAN usual; 6, ENLARGEMENT OF SURFACE OF SAME, X18, SHO\\"ING ORNAMENTATION. 



Lower part of Trenton limestone, St. Paul, Minnesota; c, fragment, xl.5, "with young Strep- 



TELASMA ATTACHED. WESENBERG LIMESTONE WESENBEEG, EsTHONIA. 



In size of zooecia and general aspect of the zoarium, P. elegans is 

 quite similar to the associated P. jldbeTlum. A surface view of the 

 zooecia enlarged, as shown in figures 62 h and 63 5, will readily dis- 

 tinguish them, since P. elegans has oval cell apertures with a well- 

 marked peristome and liighly ornamental interspaces. In thin sec- 

 tions P. Jlahellum shows the regular oval zocBcia of Pachydictya, but 

 at the surface they appear to be inclosed in rather regular hexagonal 

 areas formed by the union of the lines in the interspaces. All of the 

 other Baltic species of Pachydictya have larger zooecia. 



Occurrence. — Abundant in the CHtambonites bed of the lower 

 Trenton of Minnesota and Iowa. Fairly abundant in the Kuckers 

 shale (C2), Baron Toll's estate, and in the Wesenberg limestone (E) 

 at Wesenberg, Esthonia. 



Plesiotype.—Csit. No. 57234, U.S.N.M. 



Specimens and thin section from the Wesenberg limestone at 

 Wesenberg in the collections of the British Museum. 



92602°— Bull. 77—11 11 



