136 BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



in 2 mm. measuring longitudinally. Indeed the apertures show the 

 same variation as exhibited in the several illustrations of the f ollo%ving 

 P. varia. 



Aside from the larger zooecia the internal structure is also much as 

 in P. varia. In vertical section the zocecial tubes proceed to the sur- 

 face in a long, gentle curve. Neither diaphragms nor hemisepta 

 have been observed in any of the sections. The zooecial interspaces 

 are filled with a dense, laminated tissue which, as shown in figure 59, 

 is pierced by numerous tubuli. In tangential sections these tubuli 

 appear as dark spots or pores, numerous in the maculse, but less 

 common between the zooecia. The zooecia in such sections are 

 rounded to elongate oval and drawn out anteriorly with the walls 

 thickened by the interzooecial deposit of tissue. 



Compared with P. varia, the only other Russian species of the genus, 

 P. fiabellaris has larger zooecia, a broader and thicker zoarium and 

 more conspicuous maculae. Other bifoliate bryozoans of the Baltic 

 area are too different to require comparison. 



Occurrence. — Not uncommon in the Orthoceras limestone (B3) on 

 the island of Rogo, near Baltischport; also at Baltischport, and at 

 Tischer, near Reval, Esthonia. 



Coty pes.— Cat. Nos. 57230, 57231, U.S.N.M. 



Thin sections of specimens from Baltischport are in the British 

 Museum's collection. 



PHYLLODICTYA VARIA Ulrich. 



Text fig. 60. 



Phyllodivtya varia Ulkich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 

 1893, p. 144, pi. 14, figs. 1-8. 



A second species of Phyllodictya in the Middle Ordovician strata of 

 Russia differs conspicuously from the preceding form in having 

 smaller zooecia and a more delicate zoarium. This particular species 

 was found to agree in all essential respects with the very common 

 Minnesota Ordovician form described by Ulri,ch as Phyllodictya vafia. 

 In fact, the similarity is so great that it was thought unnecessary to . 

 show any other illustrations than those given by Ulrich. The zoarium 

 is of bifoliate, thin, leaf-like expansions, with sharp, fionporiferous, 

 subparallel edges. Scattered over the celluliferous surfaces at dis- 

 tances of about 4 mm. are solid, finely granostriate maculse which, 

 in old specimens, as shown in figure 60 e, are of considerable size. 

 The normal shape and arrangement of the zooecia, with their surface 

 ornamentation, is shown in figures 60 c and 60 d, while the usual 

 views seen in vertical and tangential sections are reproduced in figures 

 60/ and g. Measuring longitudinally, five to six apertures may be 

 counted in 2 mm. 



