PROBLEM OF THE MONTICULIPOROIDEA 153 



by mesopores, become oval and thick walled. They grow slowly 

 in the peripheral region, to 1 or i.5 mm in length with slightly 

 increasing size. They have a few thin tabulae, the first one in 

 or near the axial part, the last one often at the aperture. The 

 mesopores are small, numerous, closely tabulated, either distinct, 

 or the tabulae of neighboring mesopores overlapping in vesicu- 

 losa way, or again in maturer stages they fill with granulose 

 schlerenchyma. Mesopore walls are nearly always reduced so 

 that those between mesopores are extant only vertically in 

 zoarial direction, but mesopore corners and junction of mesopore 

 walls to autocell waU are always partly developed. Mesopores 

 are rarely distinct at the surface, and their space appears solid 

 between autocells. 



The arrangement of the cells is regular, alternating in verti- 

 cal rows, and the surface pattern is easily used to distinguish the 

 species. Maculae or solid spots of filled mesopores and filled 

 cells too, are regularly distributed over the surface and next to 

 these the cells are a little larger sized. No cell increase is seen 

 normally in the peripheral or mature region, not even in the 

 maculae. 



The best specimens only show the peristome or circular wall 

 margin papillose, and the interspaces or mesopore tabulae granu- 

 lose, or, when some walls are present, granostriate, as the 

 maculae and zoarial solid border usually are also. The preserved 

 edge of a growing mesial (or median) lamina, I have not seen, 

 but it was probably papillose. Corresponding to these structures, 

 sections show so-called vertical or median tubuli in the midst of 

 the double autocell wall, similar less distinct structures in the 

 schlerenchyma of filled mesopores, and large ones in the mesial 

 lamina. Warts and so-called tubuli on the interspaces sometimes 

 represent reduced mesopore walls. Further details, dimensions, 

 etc., characterizing the species may be passed over here. 



One finds characters in Pachydictya foliata Ulr., such only as 

 seen in Trepostomata also : bifoliate zoaria [e. g., Ceramophytta) , 

 occur among them also : axial and peripheral region, autocells 

 and vesiculose mesopores {Prosopora, Fistulipora), and maculae 



