164 Cincinnati Society of Natural History. 
described by me in the second volume of this publication, under the 
name of Chetetes elegans. The zoarium of this species consists of a 
free and very thin circular expansion, with an average thickness of .02 
of an inch, the diameter of the few specimens found varying from .4 to 
1.2 of aninch. The under surface is covered by a smooth or concen- 
trically striated, thin epitheca. The upper surface is elevated at inter- 
vals of .14 of an inch, measuring from center to center, into low and 
rounded monticules, the bases of which may be said to be in contact, 
since the interspaces are concave. Their arrangement is in concentric 
series around the central monticule, each being occupied by cells 
which gradually enlarge in diameter from ;4+5th of an inch at the base 
to ~jth of an inch at the summit.. The cells have thin walls, are rhom- 
boidal or hexagonal in shape, and arranged in regular decussating 
series, that remind one strongly of the cell-arrangement in Pétlodic- 
tya pavonia. D’Orb. In longitudinal sections (PI. VII., fig. la) the 
tubes are seen to proceed to the surface with a slight inclination; the 
walls are of medium thickness, and show more or less distinctly the 
original line of demarcation between adjoining tubes. Two or three 
diaphragms cross each tube, on lines parallel with the upper surface. 
Tangential sections (Pl. VII., fig. 10) show that the cell-watls of 
adjoining tubes are not fused together, the line of separation being 
quite distinct. On each side of this central line is the original wall, 
which is usually thickened inwardly, by a thin secondary deposit of 
sclerenchyma. The cells occupying the monticules are marked by 
thinner walls, being cut at a deeper level than those in the intervening 
space. Sections of this species prove that interstitial cells are entirely 
absent, no young or small cells of any kind having been observed. 
Spiniform tubuli are also wanting. 
Discotrypa elegans is a rare fossil in the Cincinnati group, at an 
elevation of 300 feet above low water mark in the Ohio river, at the 
quarries back of Cincinnati, O., and Covington, Ky. . 
The genus is probably more nearly allied to Leptotrypa than to any 
other genus of the Monticuliporide. They are, however, amply dis- 
tinguished by the difference in their cell structure, different habits of 
growth, and the absence of spiniform tubuli in Discotrypa. 
ASPIDOPORA ARCOLATA, n. gen. et sp. (Pl. VII, figs. 2, 2a, 2b and 2c.) 
Gen. char. ante vol. v., p. 155. 
Zoarium consisting of very thin, convex, free expansions, from .3 to 
1.0 of an inch in diameter, and about .025 of an inch in thickness. 
The under surface is marked with radiating strive, and sometimes with 
obscure concentric wrinkles. The upper or celluliferous surface 
