138 



BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



narrow with subparallel margins and the longitudinal arrangement 

 of the zocBcia predominates. The type species of the genus has a 

 broad, palmate zoarium, but its internal structure is essentially the 

 same as in the narrow, branched forms. The zooecial apertures in 

 Padiydictya are oval and have well-marked, ring-like walls, this 

 character alone being so marked that it serves as a distinction from 

 other genera of the RMnidictyonidge. 



Genotype. — Padiydictya rohusta Ulrich. Middle Ordovician (Ot- 

 tosee) shales of east Tennessee. 





Fig. 61.— Pachydictya elegans.— a, tangential section, X18, cut obliquely so as to showpabts of 



BOTH SIDES OF THE ZOAKIUM. THE UPPER THIRD EXHIBITS THE STRUCTURE OF THE FULLY MATURED 

 ZONE, WHILE A LESS MATURE PORTION IS SHOWN IN THE LOWER PART. THE SHADED AREA WITH SHORT, 

 PARALLEL LINES REPRESENTS THE MEDIAN LAMINA WITH ITS LONGITUDINAL TUBULI; 6, A SINGLE ZOOECIUM 

 OF THE SAME SECTION, X35. ClITAMBONITES BED OF LOWER TRENTON, ST. PAUL, MINNESOTA. C, 



transverse section, xls, pachydictya foliata, showing the median tubuu distinctly. black 

 River (Decorah) shales, St. Paxil, Minnesota. (After Ulrich.) 



PACHYDICTYA ELEGANS Ulrich. 



Text figs. 61, 62. 



Pachydictya elegans Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 

 1893, p. 154, pi. 8, figs. 18, 19; pi. 9, figs. 8, 9. 



Among the several species of Pachydictya found in the strata of 

 the Baltic provinces is one represented by a few well-preserved speci- 

 mens which I am unable to distinguish from the abundant form in 

 the Clitambonites bed of Mnnesota described by Ulrich as P. elegans. 

 Views of an American and a Russian example are given in figure 



