BRYOZOA. 293 



Batostoma montuosura,] 



the zooecial walls seemingly in contact in most cases, the mesopores few, and the 

 acanthopores indistinct. This condition, which is to be counted as rare, corresponds 

 to fig. 18. From it the usual deviation consists in the rounding and constriction of 

 the zocecial apertures, and widening of the interspaces. When carried to the extreme 

 we have subcircular apertures enclosed by a thin peristome, separated by depressed 

 interspaces in which the mouths of a few mesopores may be noticed. In all these 

 conditions (corresponding to figs. 16, 19, 20 and 21) the average number of zorecial 

 apertures in 3 mm. is nine or ten. The acanthopores also are rarely very conspicu- 

 ous for size, though they are numerous enough and may be distinctly visible on well 

 preserved examples. But in a variety, or rather an occasionally observed condition 

 of the species, the acanthopores are much larger and situated three or four in the 

 now thin walls of each zooecium, causing their apertures to be more or less 

 indented at the points occupied by them. 



Internal characters: The extreme variability of tangential sections is well shown 

 in the seven figures on plate XXV. And yet the species is an easy one to identify by 

 means of thin sections. Each tangential section will show from two to four of the 

 conditions illustrated, and although I used five specimens and six sections I might 

 have obtained an equal range of variation with two of them. The greater part of 

 them vary between the appearances represented in figs. 16, 19 and 21. Vertical 

 sections are more constant, having numerous diaphragms about four in the zooecial 

 tubes and six in the mesopores in 0.5 mm. in the peripheral region, and none in 

 the axial. The usual irregularity of the tubes in the axial region is noticeable. 

 Also a peculiar moniliform structure of the walls in the peripheral region is the 

 probable cause of some of the variations noticed in tangential sections. 



The zoarial growth is less robust and the average size of the zooscia less than 

 in B. fertile. The opposite is the case when compared with B. winchelli, which, like 

 B. minnesotensis, has also much fewer mesopores. The species is evidently a fore- 

 runner of B. humile of the Galena shales and B. jamesi Nich. sp. of the Cincinnati 

 rocks. 



Formation and locality. Moderately abundant in the middle third of the Trenton shales at Min- 

 neapolis and St. Paul, Minnesota. 



Mus. Beg. No. 8135. 



BATOSTOMA MONTUOSUM, n. sp. 



PLATE XXV, FIGS. 26-28. 



Zoarium ramose, small, branches dividing rapidly, 5 to 10 mm. in diameter; 

 surface with more or less conspicuous monticules, 2.0 or 2.5 mm. apart, occupied by 

 apertures of the same size as those in the depressions; the summit of the monticules 



