EAKLY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 263 



ture is brought out in figures 151 and 153. The latter thin sections 

 were prepared from an example showing the base overgrown with 

 small cells. The tangential section (fig. 153 a) passes through this 

 layer of small cells and through the adjoining normal zooecia. The 

 forms differ from the latter simply in their small size and greater thick- 

 ness of walls. In vertical sections, however, they show more resem- 

 blance to mesopores in being closely tabulated. This is illustrated 

 in figure 153 d. Figures 153 6 and c show an occurrence of the 

 diaphragm in which the free ends are either sharply bent downward 

 or have strings of tissue dependent from them. That the latter is 

 sometimes the case is evidenced in figure 153 c, where five such pro- 

 jections are noted on the lowest diaphragm. 



In growth Esthoniopora communis is exactly like Dianulites -petro- 

 politana, and the size, shape, and general aspect of their zooecia in 

 surface views are identical. After comparing 

 the figures of their totally different internal 

 structure one is impressed by the necessity 

 either of thin sections or of other means to ex- 

 amine the microscopic characters of fossil Tre- 

 postomata. With regard to all other Trepos- 

 tomata the incomplete diaphragms and amalga- 

 mated walls of the present form are the best 

 distinguishing characters. Comparisons with 

 Esthoniopora curvata are included under its de- 

 scription. 



Occurrence. — ^A common fossil in the Glauco- ^i«- i55.-esthoniopora 



..,. . /-rtc^\ J -r, 1 ii/^1 1 COMMUNIS. An UNUSUAL 



nite limestone (132) at Keval and at Oberchowow, formofzoarium.natukal 

 on the river Wolchow; in the Orthoceras Hme- ^^^^- Muckers shale 



.p, _^ -._ . .^ (02), ERRAS, ESTHONIA. 



stone (133) at rort Kunda; m the Jiichinospher- 

 ites limestone (Cl) at Reval and 4 miles east of Reval, at Katlino, and 

 at Luggenhusen; in the Kuckers shale (C2), Baron Toll's estate, near 

 Jewe, and at Erras; in the Jewe limestone (Dl), Baron Toll's estate. 



Cotypes.—Csit. Nos. 57357 to 57365, U.S.N.M. 



British Museum, specimens and thin sections from various locali- 

 ties in Esthonia. 



ESTHONIOPORA CURVATA, new species. 



Text fig. 156. 



In thin sections this species, with its long, slightly curved, cysti- 

 phragmlike, incomplete diaphragms, seems clearly distinct from the 

 preceding E. communis, although externally the two are practically 

 identical. A slight increase in the average size of both the macular 

 and intermacular cells is apparent upon close measurement, but this 

 aids little in the discrimination of the two species. However, ver- 

 tical fractures showing the different style of tabulation will distin- 

 guish E. curvata at once. The fact that the incomplete diaphragm 



