BRYOZOA. 343 



growth are frequent. Thus, in Crepipora, lamellate, discoidal, 

 and massive species occur, while a ramose zoarium character- 

 izes species of Diamesopora. The bifoliate and frondescent styles 

 of growth are also met with. The zocecia usually form short 

 tubes, but in Crepipora, Anolotichia and Chiloporella, they 

 are much longer and occasionally traversed by a small number 

 of diaphragms. A complete peristome sometimes surrounds 

 their apertures, but in most cases, only the posterior margin 

 projects. The lunarium. which is situated on this side, is nearly 

 always easily recognized, being of a decidedly lighter color in 

 sections than the rest of the zooecial investment. The irregu- 

 larly laminated construction of the walls, which appear also to 

 have been minutely porous, is the most striking, as well as, the 

 most constant character. The irregularity of the mesopores 

 and the absence of diphragms in them are other features that 

 aid in distinguishing this peculiar family of Silurian Bryozoa. 

 The affinities of the family are clearly with the FISTULIPORIDJE, 

 and the superficial resemblance between, for instance, (eramo- 

 porella and Eridopora is very marked, yet the internal char- 

 acters above mentioned are so constant and distinctive that 

 they demand recognition. 



(9) FISTULIPORID.E. In this large and important family the 

 zoarium varies greatly, but the massive and laminar with a 

 rugosely wrinkled epitheca on the under side, are the common- 

 est forms. Bifoliate and ramose species are less frequently met 

 with. The zooecia too vary considerably in the form of the 

 aperture, but in a majority of cases it is sub-oval, or sub-trian- 

 gular. In other cases the sub-pyriform or circular aperture 

 may prevail. Usually the apertures appear oblique, the degree 

 of obliquity being largely governed by the relative prominence 

 of the lunarium or hood. When they appear direct, the lunar- 

 ium is as a rule obsolete. Diaphragms are rarely numerous 

 being in most cases almost absent. In the perfect and mature 

 condition the interspaces always seem solid at the surface and 

 frequently granulose. Thin sections, however, show that the 

 zooecia are always separated from each other by from one to 

 three rows of vesicular cells, which, near the surface of mature 

 examples, are nearly or quite filled by a deposit of vertically 



