BRYOZOA. 279 



Callopora umhilata.] 



mature size, the tube is crossed by from ten to twenty or more closely and regularly 

 arranged diaphragms. After this the diaphragms are much farther apart, and in 

 many tubes may be wanting entirely until they enter the peripheral region when 

 they once more come close together. 



This species is distinguished from C. undulata by its slightly larger size, smooth 

 surface, and slight differences in the tabulation of the tubes. In tangential sections 

 the zooecia of that species are less rounded. C. goodhuensis and C. ampla have fewer 

 mesopores and more abundant diaphragms. 



Formation and locality. Rather rare in the lower third of the Trenton shales at Minneapolis, 

 St. Paul and Preston, Minnesota. 



Mus. Reg. No. 7653. 



CALLOPORA UNDULATA Ulrich. 



PLATE XXII, FIGS, il-31. 



Callopora undulata ULRICH, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Sur. Minn., p. 95. 



Zoarium ramose, branches slender, averaging about 2.5 or 3.0 mm. in diameter, 

 dividing dichotomously at intervals of 10 mm. or more. Surface with rather large, 

 rounded monticules, that usually coalesce laterally, forming transverse ridges, or 

 more or less complete annulations, five in ten mm. In some fragments and portions 

 of others the monticules are separate, while in a few they are nearly obsolete. Zooecia 

 with moderately thin walls, subangular or ovate apertures, of nearly equal size over 

 all portions of the surface ; ten or eleven in 3 mm. Mesopores comparatively few, 

 small, not readily distinguished externally, their mouths usually closed. Zooecial 

 covers not observed. 



Internal characters: These are sufficiently shown in the illustrations, and, as 

 they are also very similar to those of the preceding species, I shall only point out 

 the differences. The walls in tangential sections are thicker than in C. incontroversa, 

 the divisional line between adjoining zooecia more distinct, and the mesopores less 

 numerous. 



C. anyularis has a smooth surface, fewer mesopores, and more crowded dia- 

 phragms. C. ampla is distinguished in like manner, and C. incontroversa, externally, 

 by its smooth surface and more rounded zooecial apertures. 



Formation and locality. Not uncommon in the upper part of the middle third of the Trenton shales 

 at Minneapolis and St. Paul, Minnesota. 



Mus. Reg. No. 8113. 



