OF DENISON UNIVERSITY. 
151 
I. Phylloporina angulata, Hall. 
{Plate XV, Fig. i ; Plate XVII, Fig. i.) 
^ Retepora angulata ?, Hall and Whitfield (J?. Daytonensis proposed), 1875; 
Ohio Pal. Vol. II, p. III. 
Retepora angulata, Hall, 1882 ; 12th Ann. Geol. Rep. Indiana, p. 269. 
Frond found in flabellate fragments, originally perhaps infundi- 
buliform, reticulated by the anastomosing of the dichotomously divid- 
ing stems, forming elongated fenestrules, which are of small size to- 
wards the base of the frond, increasing in size above ; fenestrules from 
the same portion of the frond of about the same size. Poriferous side 
strongly convex, the non-poriferous side much less convex, and finely 
striated longitudinally. The cells are separated only by the cell-walls 
below, above they become constricted, opening upon the surface as 
small, rounded apertures which are more or less removed from each 
other, the intermediate portion seems often to be occupied by short in- 
terstitial cells not visible at the surface. The cells are arranged in 
four rows along the stems, the lateral rows opening directly upon the 
fenestrules. Cross-sections show that the two lower rows arise along 
the middle of the non-poriferous side and extend along the 
same to the lateral apertures, the two middle rows arise very near the 
origin of the lower rows, and open along the upper side of the stem. 
Partition walls extend longitudinally between the cells ; in division, 
the middle wall usually divides dichotomously and terminates at the 
origin of the new branches, the two lateral walls form the central par- 
tition wall of the new branches ; the lateral partition walls in the branch- 
es seem to arise from the middle wall by lateral division. During an- 
astomosis, one or the other of the stems seems to prevail and to give di- 
rection to the cells of the new structure. 
The ordinary variety of this species is of common occurrence, 
and is characterized by rather stout stems anastomosing at comparative- 
ly short intervals ; another variety with equally stout stems has much 
more elongated fenestrules, 3 mm. or even more in length. The va- 
riety for which the name R. Daytonensis was suggested has very nar- 
row branches, about .25 mm. broad, forming fenestrules 2.5 mm. long. 
This form is said to differ from the typical forms of Ph. angulata in 
‘^not possessing the angular ridges between the pores, and in having 
the borders of the pores elevated, forming the spur-like projections 
which that species does not show.” In our specimens a nodose ridge 
