278 THE PALEONTOLOGY OF MINNESOTA. 



LOallopora incontro versa. 



0.2 mm. apart. In tangential sections of fully matured examples (fig. 39) the zooecia 

 are decidedly angular, subequal, most of them in contact on all sides, the mesopores 

 being small, very few, and sometimes restricted to certain spots where limited 

 clusters may be found. 



Both the mesopores and diaphragms are less numerous than in C. muUitabulata; 

 the angular shape of the zocecial aperture will distinguish the species from other 

 forms of the genus. I found it diflficult to separate slightly abraded specimens of a 

 small form of Bcdostoma, near B. winchelli, from those of the present species. When 

 unworn the Batostoma has distinct acanthopores which are a suflBcient mark, and 

 when these have been removed by abrasion the student may succeed in separating 

 them by measurement, the latter having eleven or twelve zooecia where C. angularis 

 has nine or ten. 



Formation and locality .—'Ra.thei rare in the lower third of the Trenton shales at Minneapolis, 

 Chatfleld, and near Fountain, Minnesota. 



Mus. Reg. Nos. 8088, 8097. 



Callopoka incontroveesa Ulrich. 



PLATE XXH, FIGS. 33-36. 



Callopora ineontroversa Ulrich, 1886. Fourteenth Ann. Eep. Geol. Nat. Hist. Sur. Minn., p. 96. 



Zoarium ramose ; branches smooth, subcylindrical, 4.5 to 6 or 7 mm. in diameter, 

 dividing dichotomously at intervals of 12 or more mm. Zooecia with walls compar- 

 atively thin ; apertures oval or subcircular, rarely polygonal ; small, inconspicuous, 

 and rather irregularly distributed clusters consisting of openings slightly larger than 

 the average occasionally present; about ten apertures in 3 mm. Closures occa- 

 sionally preserved ; central perforation larger than usual, 0.07 to 0.08 mm. in 

 diameter, enclosed by a thickened rim ; apparently not radially marked, Mesopores 

 numerous, small, scarcely gathered into clusters, usually occupying only the spaces 

 left between the contiguous rounded walls of the zooecia. 



Internal characters : Tangential sections show that the zooecia are broadly 

 elliptical, rather thin-walled, and usually in contact with each other at as many 

 points as their rounded form will admit. Interspaces occupied by the mesopores. 

 At unequal intervals the latter may be more numerous and the zooecia a little 

 larger than usual, but these clusters are never conspicuous. In vertical sections the 

 tubes form a gradual but rather short curve to the surface. In their tabulation and 

 general appearance the proximal ends of the zooecial tubes are so much like the true 

 mesopores of the peripheral region that we cannot escape the conviction that their 

 functions also were alike. From the point of origin till it has attained nearly its 



