312 THE PALEONTOLOGY OF MINNESOTA. 



[CoBstellaria varla. 



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 lev6l of the maculae, but as a 

 rule the entire surface may be said to be even. In a few cases however the maculae 

 themselves are higher than the spaces separating them. Zooecial 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 8 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 (xS-) with small apertures and wide interspaces; " 

 fig. 2 a small part of another (xl8) having comparatively large zooecial apertures 

 and correspondingly narrow interspaces. The latter are always a little depressed, 

 and, like the maculae, 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 zooecial tubes and 

 interspaces depends largely upon age, the width of the zooecia 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 zooecial 

 tubes bend to the surface. In the mesopores, which are very abundant, especially 

 when the section passes through one of the maculae, 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 zooecia, 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 maculae. 



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, 813a 



