280 THE PALEONTOLOGY OF MINNESOTA. 



[Cailopora niultitabulata. 



Callopora mdltitabulata Ulrich. 



PLATE XXIII, FIGS. 11, 12, 16, 17, 24, 25, 26, 30, 31. 



Monotrypella multitabulata Ulkich, 1886. Fourteenth Ann. Eep. Geol. Nat. Hist. Sur. Minn., p. 100. 



Zoarium consisting of more or less irregularly divided, subcylindrical branches, 

 their diameter averaging 7 or 8 but varying betvsreen the extremes of 3 and 10 mm. 

 Surface generally with more or less strongly elevated, conical or rounded monticules, 

 2.5 mm. from center to center. The typical form of the species occurs in the Trenton 

 of Kentucky and Tennessee, and in the upper third of the Trenton shales of Minne- 

 sota. In this monticules are always present, and they are occupied by zooecia but 

 little if at all larger than the average. Mesopores are exceedingly few at the 

 surface, the zocecia being angular, in contact with each other, their walls thin ; 

 apertures direct, with an average of eleven in 3 mm. Closures preserved in a few 

 specimens, ornamented as shown in fig. 26. In the underlying middle third of the 

 shales and in the overlying Galena shales there is a form, rare in the first, exceed- 

 ingly common in the second, that varies in having the monticules lower and even 

 quite inconspicuous, the zooecia a little larger (ten in 3 mm), and the cells occupying 

 the low monticules usually well distinguished by their size. Very frequently too a 

 sprinkling of mesopores is detectable at the surface, as shown in fig. 31, but it is rare 

 to find them as numerous as in fig. 30. 



Internal characters: In tangential sections of the typical form the zocecia are 

 regularly polygonal, generally in contact .with each other on all sides, and provided 

 with moderately thickened walls, in which the original boundary line between the 

 zooecia is preserved as a sharp dark line. Mesopores are very few. Because of a 

 lack of room no section of this form was illustrated, but a good idea of its appear- 

 ance may be gathered from fig, 39 on plate XXII, and the upper third of fig. 17 on 

 plate XXlII, In the Galena shales variety the appearance of tangential sections is 

 generally as in the mentioned fig. 17. 



In vertical sections (pi. XXIII, fig. 24) the peripheral region is comparatively 

 wider than in other species of this type. Diaphragms exceedingly abundant 

 throughout the tubes, the average distance between them in the axial region being 

 about equal to their diameter; in the peripheral region twelve to sixteen occur in 1 

 mm. Here many of them may be slightly curved or joined to one another. An 

 occasional mesopore is met with in these sections. These are very closely tabulated, 

 the average number in 0.5 mm. being ten. Now and then one of the mesopores 

 may widen and assume the characters of a true zooecium. 



In the central part of transverse sections the size of the tubes and the appear- 

 ance in general is intermediate between figs. 20 and 21 of plate XXIII. 



