NicKiESANDBAssLER.] DIAGNOSES OF GENERA. 37 



side of the zonecium strengthened by a calcareous deposit, solid or 

 vesicular in nature, which, as it proceeds, leaves an opening- above the 

 oritico, thus producing a shaft or vestibule, which may be crossed by 

 diaphragms or hemisepta. 



Family PHYLLOPORINID^ TJlrich. 



Zoarium branching; branches free or anastomosing, celluliferous 

 on one side only, the other side striated; zocecia more or less tubular, 

 often with diaphragms; hemisepta wanting. 



Phylloporina Ulrich. 



Zoarium with branches irregularly anastomosing, with two to eight 

 rows of apertures on the obverse side, on the reverse longitudinally 

 striated; tabulated interstitial spaces generalh^ present, closed at the 

 surface; acanthopores often present. 



Genotype: Retepoi^a trentonensis Nicholson. Ordovician, Silurian. 

 Fifteen described and four new species. 



Drymotrypa Ulrich (Thamnocella Simpson). 



Zoarium branching dichotomously at frequent intervals, on reverse 

 longitudinally striated; zocecia in several ranges, tubular, springing 

 from a thin double plate, beneath which a number of vesicles (aborted 

 zocecia are present; vestibules expanding from the orifices to the 

 angular apertures. 



Genotype: Betepora diffusa Hall. Ordovician, Silurian. Four 

 Bpecies. 



Family FENESTELLIDiE King. 



Zoarium a reticulated expansion, celluliferous on one side only, 

 composed of rigid branches, united by regular nonporiferous ))ars 

 (dissepiments), or branches may be sinuous and anastomose at regular 

 intervals, or may remain free; zocecia oblong, quadrate, or hexagonal 

 in outline, embedded in a calcareous crust which is minutel}' porous, 

 especially on the noncelluliferous side; orifice anterior, semielliptical, 

 truncated behind; apertures rounded, with peristome and closed at 

 times by a centrally perforated closure; a superior hemiseptum gen- 

 erally present, an inferior one less frequentlv. 



Fenestella Lonsdale (Actinostoma Young and Young, Flabelli- 



PORiNA Simpson). 



Zoarium flabellate or funnel shaped, celluliferous on the inner side; 

 branches generalh^ straight, sometimes flexuous, connected at regular 

 intervals by dissepiments; apertures in two rows, separated by a 

 plain or tuberculated median keel. 



