Gexeka of the ^orth American Palaeozoic Bryozoa. 577 



MoNTicuLiPOBA, D'Orbigny. 



(Prod. 2, p. 279. 1847.) 



Type, Monticulijpora mamillosa, D'Orbigny. 

 (Plate 17, figs. 1-3.) 



Zoarium massive, lobate, laminar, incrusting and sometimes 

 irregularly frondescent. Cells tubular, polygonal, arising from 

 an imaginary axis at the center of the frond, gradually diverg- 

 ing until near the surface when they more abruptly turn outward, 

 at the same time becoming slightly thickened. Immediately 

 above the point of gemmation the young cell or tube is crossed 

 by numerous straight diaphragms, giving to it the appearance of 

 a mesopore, subsequently the tabulae become less crowded and 

 the tube assumes the character of an ordinary cell. In addition 

 to the diaphragm numerous cystiphragms are developed in the 

 greater number of cells ; surface with numerous conical monti- 

 cules closely and subregularly disposed in intersecting rows. 



This genus is distinguished from Homotrypa by the much 

 greater number of diaphragms and cystiphragms in the thin 

 walled portion of the cell tubes, and the absence of the thicken- 

 ing of the cell walls in the peripheral region of the frond that is 

 characteristic of Homotrypa. 



Family Amplexoporidae, Ulrich, emend. 

 This family includes, the forms which have a general resem- 

 blance to the Monticuliporidse, and essentially the same mode of 

 growth, but the cell tubes are without cystiphragms. The fol- 

 lowing genera are included in thefamily : Amp^ixopora, Dekayia, 



MONOTBYPA, MONOTRYPELLA, LEPfOTfiYPA, PeTALOTRYPA and StBN- 

 OPOBA. 



Amplexopora, Ulrich. 

 (Jour. Cin. Soc. Nat. Hist., Yol. Y, p. 154. 1882.) 

 Type, Amplexopora cingulata^ Ulrich. 



(Plate 17, figs. 6, 7.) 



Zoarium ramose or massive ; cells polygonal, forming prismatic 



tubes, which arise from an imaginary axis at the center of the 



frond, gradually diverging till within a short distance of the 



surface, when they turn more abruptly outward. In the axial 



73 



