220 THE PALEONTOLOGY OF MINNESOTA. . 
{(Monticulipora arborea. 
of the figure is taken from the lower part of the section where the transverse parti- 
tions are less closely arranged than near the surface of the zoarium. The walls have 
a lineo-granose structure. Tangential sections show that the zoccial tubes are 
polygonal and thin-walled, the opening left by the cystiphragms ovate or sub- 
ciicular and situated laterally or subcentrally. At the angles of junction the walls 
are slightly thickened, and there is some evidence to show that very small acantho- 
pores were developed at these points. 
This fine species has an external resemblance to irregular examples of M. levis 
Ulrich, from the Cincinnati group of Ohio, but the zocecia and internal structure of 
M. grandis are so much larger and different that the relation between the two species 
must really be quite remote. Excepting that mesopores are wanting entirely, the 
interior, as brought out by thin sections, is very similar to Prasopora contiqua Ulrich, 
and I have considered the advisability of referring the species to Prasopora rather 
than Monticulipora. For the present, however, we must conclude that the absence 
of mesopores and lobate-massive instead of discoid growth are features sufficient to 
disbar the species from Prasopora. 
Formation and localtty.—At the base of the Trenton shales and the top of the underlying limestone 
at Minneapolis and Cannon Falls, Minnesota. Vertical range apparently very limited. 
Mus. Reg. No. 5969. 
MonvicuLipora ARBORKEA, 7”. Sp. 
PLATE XX, FIGS. 1-9 and 138, 14. 
Zoarium dendroid, rising to a hight of 4 or 5 em.; branches subcylindrical, 
dividing at intervals varing between 5 and 20 mm.; surface with low monticules, or 
smooth. Zoccial apertures small, subangular, enclosed by rather thick, minutely 
eranulose walls, on which small acanthopores, one or two to each zocecium, are to be 
distinguished from the numerous small granules, which, together with the acantho- 
pores, are quickly removed when exposed to the weather. About fourteen of the 
cells between those occupying the monticules or those in the clusters occur in 5 mm. 
Mesopores wanting. 
Internal characters: The tabulation of the zocecial tubes is compact throughout, 
and very much so in the peripheral region. The tubes bend outward in a gradual 
curve from the imaginary axis, and have cystiphragms from the beginning. In the 
axial region these are large and about two-thirds of the tube-diameter apart, becom- 
ing gradually a little nearer to each other until the fully matured condition of, the 
species is reached, when they recur at intervals scarcely equalling one-fourth of the 
diameter of the tube. They also change their shape here, the opening which had 
