NicKLESANDBASsLER.] DIAGNOSES OF GENEKA. 35 



DiTTOPOliA Dybowski. 

 Family TREMATOPORID^ Ulrich. 



Zoiiriuni ramose or iiu'rustint^; zo(Bciii irregular in axial region, their 

 proximal ends with diaphragms and usually constricted where these 

 occur; walls thickened in the mature region; lines of contact of walls 

 of adjoining zooecia distinct; mesopores generally abundant, usually 

 of large size, closed at the surface; acanthopores more or less abundant; 

 diaphragms in both zooecia and fnesopores. 



Trematopora Hall. 



Zoarium ramose; surface smooth or with monticules; zooecia thin- 

 walled and with few diaphragms; apertures circular or oval, with a 

 more or less well-marked peristome; interspaces solid; mesopores 

 irregularly angular, often obscurely moniliform, with diaphragms at 

 the constricted parts; acanthopores of medium or small size usually 

 present. 



Genotype: Trematopora U^erculosa Hall. Ordovician, Silurian. 

 Ten species. 



Batostoma Ulrich. 



Zoarium irregularly ramose, branches arising from a large basal 

 expansion; zooecia with walls that are thin in the immature region, 

 much thickened and in sections appearing ringlike (but seldom in con- 

 tact) in mature region; diaphragms present; mesopores numerous or 

 few, irregular in size or shape; acanthopores usuall}' of large size and 

 abundant, sometimes few. 



Genotype: Montlculipora {Ileterotryjya) imjjUcata^ichohon. Ordo- 

 vician. Eighteen described and fifteen new species. 



Hemiphragma Ulrich. 



Like Batostoma, but diaphragms in mature region of zooecia 

 incomplete. 



Genotype: batostoma hTa.9mn Ulrich. Ordovician. Five species. 



Stromatotrypa Ulrich. 



Zoarium consisting of one thin layer, or several superimposed, 

 growing upon foreign bodies; zooecia short, Avith few diaphragms, the 

 proximal end scarcely prostrate, oval in cross section; walls thin, con- 

 taining periodicall}^ constricted, bead-like tubuli (modified acantho- 

 pores?), one or more to each zooecium; apertures oval, separated by 

 depressed interspaces, the peristomes miiuitcl}' papillose; mesopores 

 abundant, l)eginning on the basal lamina, decreasing in size with age, 

 closely tabulate, the diaphragms finely punctured, their openings 

 rarely showing, being closed by a common dermal sheet. 



Genotype and only descriljcd species: Stromatotrijpa oixita lllrich. 

 Ordovician. Three new species. 



