168 THE PALEONTOLOGY OF MINNESOTA 
{Escharopora. 
EscHAROPORA ANGULARIS 7. Sp. 
PLATE XII, FIGS. 1-4, 30 and 31. 
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 zocecia) 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 (1) the unusual tenuity of the walls, 
and (2) the erectness of the zocecial tubes. Tangential sections greatly resemble 
such sections of certain T’repostomata (e. g. Monotrypella quadrata Rominger, sp.). 
The comparatively irregular arrangement of the zocecial 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 EF. 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 
zocecial apertures quite different. 
Formation and locality—Rare in the Trenton limestone at Minneapolis, Minnesota. 
EscHaropora susreota 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, subeylindrical, finely striated longitudinally, the grooves widening slowly 
