292 THE PALEONTOLOGY OF MINNESOTA. 



|.Bat09toma varium. 



to each zooecium rising generally from the wall at some point between the angles 

 of junction. Many of the latter are occupied by small mesopores, but these are to 

 be regarded as comparatively very few and at all times diflBcult to distinguish 

 externally. 



Internal characters: In tangential sections the tubes are polygonal and have 

 rather thin walls in which the line of contact between adjoining tubes is distinctly 

 preserved. Mesopores few, small, chiefly at the angles of junction. Acanthopores 

 small, inconspicuous. In vertical sections the tubes proceed toward the surface in 

 a very gentle curve until they enter the unusually narrow peripheral region, where 

 the curve is sufficiently accelerated to enable them to open at the surface with 

 nearly direct apertures. Diaphragms are very remote or wanting in the axial 

 region, and not numerous even in the peripheral portion. Here each tube pre- 

 sents from one to five, separated by intervals of from one-half to one tube-diameter. 

 In the mesopores, which appear to be very short, the diaphragms are much closer 

 with three or four in 0.5 mm. In the central part of transverse sections (fig. 14) the 

 tubes are conspicuously divided into a large and small set, both having very thin 

 walls. 



The large size of the zooecia distinguishes this species not only from all the 

 other forms of the genus known but from all the associated bryozoans as well. 

 Anolotichia impolita, restricted to the bed of shales immediately beneath ("Stictopo- 

 rella beds "), has zooecia fully equalling those of the present species in size, but they 

 are each provided with a lunarium and are commonly of either rhomboidal or hexa- 

 gonal shape, while the surface is without monticules and the growth of the zoarium 

 decidedly irregular. 



Formation and locality. — Four specimens were found in the middle third of the Trenton shales, 

 three at Minneapolis, the fourth at West St. Paul. 



Batostoma varium, n. sp. 



PLATE XXV, FIGS. 18-25. 



Zoarium growing from a large basal attachment into erect branches. These 

 vary in width from 7 to 20 mm. but average from 10 to 15 mm., are generally a little 

 compressed and divide most irregularly. In some cases the basal expansion consists 

 of several distinct layers, varying from 1 to 3 ram. in thickness. Surface without 

 monticules, but exhibiting instead clusters of orifices larger than the average and 

 separated by interspaces wider than usual. Not infrequently the center of these 

 clusters is marked by a small substellate solid macula. Superficial characters 

 variable, the walls in some cases being thin, with the zooecial apertures subangular, 



