NicKLESANDBASsi.ER.] DIAGNOSES OK GP:NKRA. 43 



ScEPTROPORA Ulrich. 



Zoariuni of segnients which bccoine much expanded in their upper 

 portion and at the top have a socket for the articulation of the next 

 sconient; lower portion striated, without apertures; upper part with 

 apertures all around; apertures subovate, in linear series between lon- 

 o'itudinal rido-es. 



Genot3'pe: Sceptropora facula Ulrich. Ordovician, Silurian. Two 

 species. 



Nematopora Ulrich. 



Zoarium very slender, ramose, continuous above the pointed basal 

 extremity; zooecia subtubular, arranged radially around one or two 

 minute axial tubes; apertures oval or subcircular; with peristome, 

 generally in linear series between longitudinal ridges. 



Genotype: Nematopora ovalis Ulrich. Range, Ordovician-Devo- 

 nian. Fifteen species. 



Family RHABDOMESONTID^ Vine. 



Zoarium ramose or simple, not articulated, sometimes with an axial 

 tube, but generally solid, in which case the axial region is occupied by 

 thin-walled primitive tubes, with or without diaphragms; hemisepta 

 usually present, but never conspicuous; apertures circular or oval, 

 usually in linear series between longitudinal elevated ridges, or in diag- 

 onally intersecting series; vestibule a rhombic or hexagonal sloping 

 area; mesopores generally absent. 



Rhombopora Meek. 



Zoarium slender, ramose, solid; zooecia thick-walled in vestibular 

 region; apeHures in longitudinal or diagonally intersecting series; 

 acanthopores present, sometimes of two kinds, large and small. 



Genotype: Rhoiahojxyra Itpidodendroides Meek. Range, Silurian- 

 Carboniferous. Twenty-nine described and several undescribed 

 species. 



Rhabdomeson Young and Young. 



Zoarium with a slender axial tube, to which the proximal ends of 

 the zooecia are attached; otherwise like Rhom})opora. 



Genotype: M'dlepora gracilis Phillips; from the Carboniferous of 

 England and Scotland. No American species have 3^et been made 

 known. 



Cgeloconus Ulrich. 



Zoarium simple, hollow, very gradually expanding from an attenu- 

 ated, striated base; zooecia short, with well developed hemisepta, aper- 

 tures in diagonally intersecting series. 



Genotype: Coeloconus rhornbious Ulrich. Mississippian. Two 

 species. 



