312 THE PALEONTOLOGY OF MINNESOTA. 
(Constellaria varia. 
stellate, very slightly depressed or on a level with the general plane of the surface. 
The small clusters of zocecial apertures (four to ten in each) occupying the angles 
between the rays may be elevated a little above the level of the macule, but as a 
rule the entire surface may be said to be even. In a few cases however the maculz 
themselves are higher than the spaces separating them. “Zoccial apertures subcir- 
cular, inclosed by a very thin rim, and varying considerably in size, though approxi- 
mately equal on each fragment. Width of interspaces varying correspondingly 
so that about the same number of apertures occur in a given space in all 
specimens. .Ten or eleven occur in 3 mm. in the intermacular spaces, while the 
diameter of the apertures varies between the extremes of 0.15 and 0.25 mm. Figure 1 
represents the surface of a specimen (x9) with small apertures and wide interspaces; 
fig. 2 a small part of another (x18) having comparatively large zocecial apertures 
and correspondingly narrow interspaces. The latter are always a little depressed, 
and, like the macule, occupied by the shallow yet distinct mouths of angular 
mesopores. 
Internal characters: Figure 4 represents a portion of a tangential section where 
it divides a mature zoarium immediately beneath the surface. In most sections the 
walls will be thinner and probably not show the minute tubuli in them as drawn in 
fig. 4. Series of sections prove that the relative width of the zocecial tubes and 
interspaces depends largely upon age, the width of the zoccia decreasing with 
maturity. Figure 5 is from a good vertical section, and shows that diaphragms 
occur in all the tubes throughout the zoarium, in the axial] region generally about 
twice their diameter apart, the distance between them becoming less as the zocecial 
tubes bend to the surface. In the mesopores, which are very abundant, especially 
when the section passes through one of the maculx, the diaphragms are at first 
rather far apart, but gradually become almost crowded at the surface. 
This species is nearer C. limitaris Ulrich, of the upper part of the Hudson river 
group, than any other. The superficial resemblance between them is very decided, 
but when we compare thin sections we find that the later species has smaller and 
much more abundantly tabulated mesopores. Indeed, the diaphragms are more 
numerous in both sets of tubes. All the other described species of the genus have 
smaller zocecia, and most of them differ in having no diaphragms in the axial region. 
None of the associated species are likely to be confused, none of them having 
stellate macule. 
Formation and locality.—Rather rare in the upper beds of the Galena shales near Cannon Falls, 
Minnesota. It is here associated with Orthis germana W and S., Homotrypa similis Foord, and several 
species of Nematopora. 
Mus. Reg. No. 8044, 8130. 
