BRYOZOA. 311 



invariably exhibit the exterior of the tubes. On the contrary, 

 rough fractures of Bryozoa with interstitial vesicles like Fistu- 

 lipora, Cystodictra, etc., expose the interior of the cells. I am, 

 therefore, not inclined to regard these as each having its own 

 complete investment. The only portion of the confining invest- 

 ment which can be said to be strictly its own, is the convex 

 plate which forms its upper boundary* 



If actual fusion of the walls of contiguous zooecia ever oc- 

 curs among Palaeozoic Bryozoa, it is to be looked for in the 

 CERAMOPORID.E. This family is distinguished by a wall struc- 

 ture differing obviously from that observed in such Bryozoa as 

 Leptotrypa, Stenopora, Rhombopora, Amplexopora or Bato- 

 stomella. In the CERAMOPORIDJE, namely, the walls of adjoining 

 zooecia and mesopores seem to be perfectly amalgamated, and, 

 so far as observed, rough fractures always exhibit the interior 

 of the tubes. In species with thick walls (Diamesopora coin- 

 munis) the central portion of the partitions, as seen in tan- 

 gential sections, is sometimes apparently structureless, but gen- 

 erally a more careful examination will reveal a peculiar granu- 

 lar or intermittent appearance, while in species with thin walls 

 (e. g. Crepipora simulans and C. hemispb&i-ica,) the whole wall 

 is of this composition. Very nearly the same granular wall- 

 structure is observed in species of Monticulipora, but in these 

 the duplex character of the partitions is demonstrated by rough 

 fractures. In all these cases the appearance here described as 

 granular or intermittent, is most probably due to the imperfect 

 preservation of excessively minute pores in the walls of the 

 tubes. Being a feature of some importance, it will be referred 

 to again. 



The most obvious peculiarity of the Ceramoporoid wall is 

 found in the irregularly laminated deposit immediately sur- 

 rounding the tube cavity. The lines which separate the con- 

 centric lamina* rarely extend around the wall, and in most in- 

 stances are not parallel. Sometimes they even appear to inter- 

 twine. When examined in vertical sections the walls present 

 the appearance of being composed of narrow, super-imposed, 

 alternately light and darker bands of sclerenchyma, which slope 

 backward and downward. A narrow structureless and often 

 nearly colorless band which hues the inner side of the posterior 



