168 THE PALEONTOLOGY OP MINNESOTA 



lEsrlmropora. 



ESCHAROPORA ANGULARIS U. Sp. 

 PLATE XII, FIGS. 1-4, 30 arid III. 



Zoarium simple, falciform, curved, 10 to 30 mm. or more in length, 2 to 9 mm. 

 wide; articulating base pointed, with comparatively a small part of the extremity 

 solid and striated. Zocecial apertures polygonal, commonly hexagonal, arranged in 

 transverse and diagonally intersecting series, the first predominating, and both less 

 regular than usual for the genus. Here and there the presence of one or more 

 small cells (?abortive zooecia) may cause considerable interruption in the ordinary 

 arrangement. On an average nineteen or twenty apertures in 5 mm. diagonally, 

 and nine or ten in 2 mm. transversely. Walls very thin, the thickness about equal 

 on all sides. Non-poriferous margin very inconspicuous. 



Of internal characters the most striking are (l)the unusual tenuity of the walls, 

 and (2) the erectness of the zooecial tubes. Tangential sections greatly resemble 

 such sections of certain Trepostomata (e. g. Monotrypella quadrata Rominger, sp.). 



The comparatively irregular arrangement of the zooecial apertures, their 

 angular form, and the fact that their also thinner walls commonly form hexagonal 

 or polygonal instead of subrhomboidal spaces, distinguishes this species from E.fal- 

 ciformis (Ptilodictya falciformis Nicholson) of the Cincinnati group. In other respects, 

 especially in the shape of the zoarium, the two species resemble each other very 

 greatly. Embedded in the limestone, with only a portion of the surface exposed, 

 E. angularis might very easily be mistaken for some monticuliporoid. Not so, 

 however, with E. subrecta, which abounds at the same localities though not at the 

 same geological horizon. The zoarium of the latter is always straighter, and the 

 zooecial apertures quite different. 



Formation and locality. Hare in the Trenton limestone at Minneapolis, Minnesota. 



ESCHAROPORA SUBRECTA Ulrich. 



PLATE XII, FIGS. 5-29. 



Ptilodictya subrecta ULRICH, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Sur. Minn., p. 63. 



Zoarium simple, flattened, straight or slightly curved, 12 to 40 mm. or more 

 long, 1.3 to 9.0 mm. wide, the two faces obscurely ridge-shaped, or evenly convex. 

 Average size about 25 mm. long, and 2.5 mm. wide in the upper half. Greatest 

 thickness varying with age from 0.6 to 1.5 mm. Lower half tapering gradually to 

 to the pointed basal articulating extremity, the latter often turning a little to one 

 side, subcylindrical, finely striated longitudinally, the grooves widening slowly 



