EARLY PALEOZOIC BRYOZOA OF THE BALTIC PROVINCES. 



121 



stome, which is elevated and prolonged at each end. The surface is 

 also ornamented by a thin, papillose, wavy ridge separating the 

 longitudinal rows of zooecia. The simple, unbranched segments of 

 this species with their ends rounded for articulation with each other 

 will distinguish them from all other associated bryozoans. 



Occurrence. — An abundant fossil in the lower half of the Black 

 River (Decorah) shales, in Minnesota and Iowa; apparently rare in 

 the Wassalem beds ,(D3) at Uxnorm. (Cat. No. 57212, U.S.N.M.). 



American specimens are in the collections of the British Museum. 



Genus GRAPTODICTYA Ulrieh. 



Graptodictya Ulrich, Journ. Cincinnati Soc. Nat. Hist., vol. 5, 1882, pp. 151, 

 165. — Miller, North Amer. Geol. and Pal., 1889, p. 307. — Ulrich, Geol. 

 SuTV. Illinois, vol. 8, 1890, p. 393.— Pocta, Syst. Sil. Center Boheme, vol. 8, 

 pt. 1, 1894, p. 14. — Simpson, Fourteenth Ann. Rep. New York State Geolo- 

 gist for the Year 1894, 1897, p. 541.— Nickles and Bassler, Bull. 173, U. S. 

 Geol. Surv., 1900, p. 46. — Cumings, Thirty-second Ann. Rep. Dep. Geol. 

 Nat. Res. Indiana, 1907, p. 747. 



This genus may be considered as an Arthropora with the jointed 

 character of the zoarium limited to the base alone. The zooecial 

 structure and surface ornament are alike in both genera, but the 

 rather large, single, narrow branching frond of Graptodictya with a 

 pointed, striated base articulating with a small basal expansion is 



wmm 



km 



r^< 



Fig. 47.— Graptodictya perelegans. a, tangential section, X20, of the type-specimen; b, several 

 zocECiA, X40; c, vertical section, X20; d, transverse section, X20. Richmond group, Clarks- 

 %tlle, Ohio. 



quite different from the numerously segmented method of growth in 

 ArtJoropora. 



The Russian specimens referred to the genus include a species very 

 similar in growth and other features to the American genotype, and 

 in addition two cribrose forms — a method of growth which hitherto 

 had not been recognized in the genus. The method of growth in the 

 two latter species Graptodictya proava (Eichwald) and G. oUigua, 



