312 PALEONTOLOGY OF ILLINOIS. 



wall, represents the lunarium, which (among the CERAMOPORID.E) 

 is usually distinguished from the rest of the zooecial investment 

 by its lighter color. 



The primitive duplex character of the zocecia walls of the 

 FENESTELLHLE and ACANTHOCLADIID^ is generally shown in deep 

 tangential sections, but, after they have passed into the erect 

 stage, the divisional lines are rapidly obliterated by the deposit 

 of layers of calcareous material in the spaces between the aper- 

 tures. As is seen in transverse and vertical sections, these 

 layers are deposited equally over all portions of the original 

 zooecia, appearing as parallel bands, conforming with the shape 

 of the primitive zoarium. Among the bifoliate genera of the 

 CRYPTOSTOMATA, Stictotrypa is built up upon very nearly the 

 same plan. Here, also, the originally thin cover of the zooecium 

 is thickened by the deposition of successive horizontal or con- 

 cave layers of sclerenchyma. Vertical sections of this genus, 

 therefore, are very different from those of Stictopora and Ptilo- 

 dictya, in which the walls are constructed upon the same plan 

 as in Rhombopora, etc. 



Lastly, the walls of the CYCLOSTOMATA genera Stomatopora, 

 Protocrisina, Miioclema, etc., have that finely granular appear- 

 ance in thin sections, which I consider as indicative of an 

 originally porous condition of the wall. That the walls were 

 really pierced by fine pores is clearly shown by numerous speci- 

 mens from Cincinnati, O., and elsewhere. So far as the inde- 

 pendence of the walls of contiguous zooecia is concerned, the 

 sections studied offer no positive evidence. 



c. Connecting foramina or communication pores. While evi- 

 dence showing that the zooids of a colony communicated freely 

 with each other is abundant, it is nevertheless true that it is 

 rarely or never so conclusive with Palaezoic Bryozoa as to de- 

 termine this point beyond dispute. Only now and then a speci- 

 men is found furnishing any evidence whatever to bear upon 

 the question, and in the great majority of cases the observer 

 is left in total ignorance upon this important point of bryozoan 

 anatomy. Of the most typical CYCLOSTOMATA, some of which 

 were represented in Palsezoic times, we know that the parti- 

 tions between adjoining zooecia are perforated by numerous 

 minute pores, and it is of these forms that we may regard the 

 evidence bearing upon the point in question (presented by thin 



