EAELY PALEOZOIC BEYOZOA OP THE BALTIC PROVINCES. 



131 



Fig. 55.— Stictoporella gracilis, a, tangential .section, X20; 

 6, atertica'l section, X20. Glaxjconite lime.stone (B2), Was- 



SILKOWA, government OF St. PETERSBURG. 



tissue found 'at the base of the zoarium. The internal structure of 

 the species is shown in figure 55, where the oval zooecia separated by 

 ridges and occasional mesopore-like spaces of the tangential section, 

 and the long, tubular, primitive zooecium of the vertical section are 

 the most noteworthy features. 



There is no known 

 Russian species with 

 which Stictoporella gra- 

 cilis need be compared. 

 In America its closest 

 ally seems to be Sticto- 

 porella exigua Ulrich, 

 from the lowest beds 

 of the Trenton lime- 

 stone at Montreal, 

 Canada. The latter 

 has a quite similar 

 zooecial structure, but 

 is very different in 

 zoarial growth. 



Occurrence. — Common in the Glauconite limestone (B2) at Wassil- 

 kowa, on the Lawa, Oberchowo and Tswos, on the Wolchow, and 

 Gornaja Scheldicha, on Lake Ladoga, government of St. Petersburg. 



Plesiotypes.—Csit. No. 57223, U.S.N.M. 



British Museum, specimens and thin sections from the Glauconite 

 limestone at ¥/^assilkowa. 



Family RHINIDICTYONID^ Ulrich. 



This prolific family is almost restricted to the Ordovician and 

 includes genera which, in the general shape of the zoarium, seem to 

 be little different from the various preceding Cryptostomata. The 

 zooecial structure, however, is distinctly different, the most obvious 

 points of difference being the presence of median tubuli between the 

 median laminae, and between the longitudinal rows of zooecial tubes. 

 Mesopores are absent, but the interzooecial spaces are often fitlled 

 with vesicles. 



Genus RHINIDICTYA Ulrich. 



Rhinidictya Ulrich, Journ. Cincinnati Soc. Nat. Hist., vol. 5, 1882, p. 152. — 

 Hall and Simpson, Nat. Hist. New York, Pal., vol. 6, 1887, p. xx. — Ulrich, 

 Geol. and Nat. Hist. Sm-v. Minnesota, vol. 3, pt. 1, 1893, p. 124; Zittel's 

 Textbook of Paleontology (Eng. ed.), 1896, p. 279. — Simpson, Fomteentli 

 Ann. Rep. State Geol. New York for the year 1894, 1897, p. 605. — Nickles 

 and Bassler, Bull. 173, U. S. Geol. Surv., 1900, p. 48.— Cumings, Thirty- 

 second Ann. Rep. Dep. Geol. Nat. Res. Indiana, 1907, p. 755. 



Stictopora (part) Hall, Nat. Hist. New York, Pal., vol. 1, 1847, p. 73. 



Stictopora (not Hall) Ulrich, Geol. Surv. Illinois, vol. 8, 1890, p. 388. 



This fine genus is represented in the Russian deposits by two weU- 

 marked forms, one from the Wassalem beds, which can not be dis- 



