130 NORTH AMERICAN INDEX FOSSILS. 



45. P. lycoperdon (Hall). Ordovicic. 

 Differs from preceding in absence of monticules and in large 



irregular clusters of closely tabulated mesopores, an average of 

 9 cells in 3 mm., both cells and mesopores being somewhat larger 

 than in preceding species. (The original description is applicable 

 to so many species, which have gone by this name, that many 

 authors have discarded it altogether.) 

 Trenton of New York, Canada, etc. 



XXX. Aspidopora Ulrich. 



Zoarium expanded or of superimposed layers, with a basal epi- 

 theca; zocecia decreasing in size outward from center, without 

 diaphragms and few cystiphragms ; mesopores numerous, with 

 close diaphragms ; acanthopores small or absent. Differs from 

 the preceding mainly in small size and thinness of expansion. 



46. A. elegantula (Ulrich). (Fig. 186, e.) Ordovicic. 

 Surface with large clusters of large cells at intervals of 3 or 4 



mm., generally elevated; mesopores between all zocecia; cysti- 

 phragms practically or quite wanting. 

 Trenton of Minnesota. 



47. A. newberryi (Nicholson). Ordovicic. 

 Differs from preceding in absence of elevations and in greater 



abundance of cystiphragms, which occur in each zocecium. 

 Utica beds of the Cincinnati region. 



XXXI. Mesotrypa Ulrich. 



Like Prasopora, but flatter, and with oblique or funnel-shaped 

 diaphragms, and zocecia separated by angular mesopores with 

 numerous diaphragms ; acanthopores sometimes large. Ord.-Sil. 



48. M. quebecensis (Ami). (Fig. 186,/.) Ordovicic. 

 Varying in height from 4 to 20 mm., and in diameter from 12 



to 45 mm. Normal zocecia 11 or 12 in 3 mm., those of the 

 clusters 0.4 to 0.45 mm. in diameter ; oblique diaphragms in 

 zones; acanthopores wanting. 



Trenton of Quebec, Vermont, New York, Kentucky and Iowa. 



XXXII. Amplexopora Ulrich. 

 Ramose, discoidal or massy, with prismatic zocecia with dia- 

 phragms; acanthopores variable. Ordovicic. 



