586 



Keport of the State Geologist. 



petaloid appearance ; cells with cystiphragms and occasional dia- 

 phragms ; nodes very numerous, encroaching more or less on the 

 cell cavity. 



HOMOTRYPELLA, UMch. 



(14th Kept. Geol. Sur. Minn., p. 83. 1886.) 



Type, Homotrypella instahilis, Ulrich. 



Zoarium somewhat irregularly ramose, sometimes palmate or 

 f rondescent ; surface with maculae, consisting of clusters of meso- 

 pores ; cell apertures subcircular ; mesopores abundant frequently 

 isolating the cell tubes, closely tabulate; cell tubes with dia- 

 phragms and cystiphragms, the latter being chiefly developed in 

 the median portion of the cell tubes ; usually absent just below 

 the surface and never occurring in the axial region ; surface with 

 numerous small nodes or granules. 



Fig. 168. Homotrypella instabilis. Fronds natural size . | 

 Figs. 169. Vertical and transverse sections, xl8. 



Peasopora, Nicholson and Etheridge. 



(Ann. and Mag. Nat. Hist., 4th Series, Yol. XX, p. 38. 1877.) 



Type, JPrasopora gravce, Nicholson and Etheridge. 



Zoarium forming conical, hemispherical or irregular masses, 

 the under side of the conical forms usually being concave and 

 covered with a concentrically wrinkled epitheca ; cells tubular, 

 prismatic, becoming cylindrical as they approach the surface ; 

 walls thin, with both diaphragms and cystiphragms ; mesopores 

 few or numerous, sometimes completely isolating the cell tubes. 

 In some species there are numerous spiniform nodes; surface 

 with frequent maculae of large cell apertures, or with monticules, 



