EAKLY PALEOZOIC BRYOZOA OP THE BALTIC PROVINCES. 225 



less in diameter, while the irregular nodular masses are the result 

 of either interrupted growth or of accelerated growth in several 

 directions. The zoarial surface in all the 

 various forms of growth is usually smooth, 

 but in rare instances the maculae are indi- 

 cated by slightly elevated, dome-shaped 

 areas, 3 mm. apart, measuring from their 

 respective centers. Ordinarily the macular 

 zooecia and mesopores differ so little from 

 the ordinary forms that the maculae are 

 indistinguishable at the surface. Zooecial 

 apertures direct, polygonal to rounded, four 

 in 2 mm., completely isolated by numerous small, angular mesopores. 

 In old examples the walls of both zooecia and mesopores bear 

 numerous small granules. 



Fig. 125.— Nicholsonella gibbosa. 



ElCHWALD'S FIGURES OF HeTER- 



OPORA gibbosa; a, zoarium, 



NATURAL size; 6, THE SURFACE 

 ENLARGED. " CALCAIRE k ORTHO- 



ceratites," Pulkowa, govern- 

 ment OF St. Petersburg. 



Fig. 126. — Nicholsonella gibbosa. a and &, top views of two irregular zoaria, natural size; 

 c, side view of a third specimen of more regular form; d, an example with low monticules, 

 VIEWED from above; e, tangential section, X20, through a macula; /, portion of the same 

 section, X20, cutting the ordinart zocecia; g, several zocecia, X40, illustrating the minute 

 structure; h, vertical section, X8; i, portion of the same section, X20. Glauconite limestone 

 (B2), Reval, Esthonia. 



As usual in species of the genus, the internal structure of the pres- 

 ent form, with regard to clearness of preservation, is in sharp contrast 

 with associated Trepostomata. Numerous thin sections of the 



