28 AMEBIC AN FOSSIL BRYOZOA. [bull. 173. 



Family BOTRYLLOPORID^. 

 BoTRYLLOPORA Nicholson. 



Zoarium of small, circular, parasitic disks which commonly coa- 

 lesce, developing- along the line of coalescence unusually large vesicles; 

 surface marked by ridges radiating from the depressed center and 

 increasing in iiumber by bifurcation toward the margin; zocecial tubes 

 occupying the ridges, traversed by occasional diaphragms; depressed 

 space between ridges occupied by vesicles, presenting a solid inter- 

 space; apertures in two rows on the ridges, circular or oval, with no 

 lunarium. 



Genotype and only known species: Botryllojpmn socialis Nicholson. 

 Devonian. 



Suborder TKEPOSTOMATA Ulrich. 



Zooecia prismatic or cylindrical, coherent tubes clearl}^ separable into 

 two regions, an axial or immature, in which the diaphragms are 

 remote and the walls thin and p]-ismatic, and a thickened peripheral or 

 mature, in which the walls are thickened and otherwise changed, dia- 

 phragms are more abundant, and accessory features, such as mesopores 

 and acanthopores, are often developed; zooecial covers, with a small 

 central orifice, present at times, though probably not developed in all 

 the families; monticules or maculae a characteristic feature of the 

 surface. 



Family MONTICTJLIPORID^ Nicholson (emend. Ulrich). 



Zoarium variable; zooecia with cystiphragms in the mature region 

 always; apertures polygonal, rounded or irregularly petaloid; meso- 

 pores generally present, angular, with numerous diaphragms; acan- 

 thopores abundant, usually small. 



MoNTicuLiPORA D'Orbigny. 



Zoarium massy, lobate or lamellate, incrusting or free; monticules 

 usually present; zooecia prismatic, usually thin-walled, with cysti- 

 phragms both in mature and immature regions; apertures polygonal; 

 mesopores few or wanting; acanthopores small, generally numerous. 



Genotype: lfontlctilipora'mamniulataD''Orhigny. Ordovician, ? De- 

 vonian. Sixteen described and sixteen new species. 



Atactoporella Ulrich. 



Zoarium generally incrusting, sometimes lobate or sub ramose; 

 zooecia with veiy thin, inflected walls; apertures irregularly petaloid; 

 mesopores numerous, frequently isolating the zooecia, largely filled by 

 a secondary deposit; acanthopores very numerous. 



Genotj^pe: Atactoporella typicalis Ulrich. Ordovician. Eleven 

 described and three new species. 



