BRYOZOA. 291 



Batostoma magnopora.] 



Internal characters: In vertical sections the tubes have thin and somewhat 

 irregularly fluctuating walls in the axial region. Their course to the surface is 

 gently curved throughout, and as they near the same their walls are appreciably 

 thickened, while mesopores, whose number varies greatly in different specimens, are 

 abruptly developed. The mesopores may be constricted at the points where they 

 are intersected by the diaphragms. The latter are often thickened circumferentially, 

 and vary somewhat in the number occurring in a given space, seven and eleven in 

 1 mm. being the extremes so far noticed. In the axial region diaphragms are very 

 far apart or are wanting entirely, but in the peripheral portion the average distance 

 between them is about equal to half their diameter. Specimens more than 12 mm. 

 thick consist of two or more layers of tubes. 



The four tangential sections figured on plate XXV, fully illustrate the charac- 

 ters of the species as brought out in this kind of section. Fig. 7 is from a specimen 

 with very thin walls, few mesopores, and scarcely distinguishable acanthopores, the 

 latter being in the angles of junction. Fig. 4 represents a small portion of a section 

 prepared from the original of fig. 2. In this, which is an average example, the walls 

 are thicker, mesopores more abundant, and the acanthopores, though small, more 

 readily distinguished. Minute foramina are shown in the diaphragms of some of the 

 mesopores. Figures 8 and 9 are from specimens of the variety circulare, the first 

 with thick zooacial walls, the second with them thin as in fig. 6. 



In a general way this species reminds one more of upper Hudson river species 

 than of Trenton forms. Variety circulare resembles B. manitobense Ulrich,* very 

 closely, but the clusters of large zocecia are more conspicuous in that species. The 

 typical variety on the other hand is more like B. variabile, differing from it chiefly 

 in the smaller size of the acanthopores. Compared with associated Bryozoa none 

 save Anolotichia impolita have as large zooecia. 



Formation and locality. Abundant in the lower third of the Trenton shales at Minneapolis and 

 St. Paul, Minnesota. 



MILS. Reg. No. 8136 ; var. circulare, 8137. 



BATOSTOMA MAGNOPORA, n. sp. 



PLATE XXV, FIGS. 12-15. 



Zoarium ramose; branches large, subcylindrical, 8 to 15 mm. wide; surface 

 elevated at irregular intervals into low monticules, the latter broad and occupied 

 by zocecia a little larger than the average. Zooecia unusually large, about eight in 3 

 mm., their apertures polygonal, the walls thin, with one or two small acanthopores 



*Contr. Micro-Pal. Cambro-Sil. rocks of Canada, pt. II. p. 33. 188!). 



