BRYOZOA. 295 



Batostoma wlnohelli.] 



more or less separated by partially filled mesopores. The acanthopores also increase 

 in size and distinctness but, being situated either in the interspaces or on the outer 

 side of the zooecial walls, never encroach upon the zocecial cavities. In the axial 

 region of vertical sections the tubes have irregularly undulating thin walls and no 

 diaphragms. Nor are these structures developed except in the unusually narrow 

 peripheral region, where from one to three have been observed in each tube. The 

 mesopores are very short and provided with two or three thick. diaphragms; or they 

 may appear to be filled with solid tissue. - 



The oval zooecial apertures, more slender growth, and absence of monticules 

 are the most striking differences between the present species and B. montuosum. 

 The zoarium is smaller, the branches more slender, and the peripheral region much 

 narrower than in B. varium. An undescribed variety of B. jamesi Nich. sp., occurring 

 in the Utica horizon at Cincinnati, Ohio, corresponds more nearly than any of the 

 known Minnesota species of the genus. 



Formation and locality. — Moderately abundant in the Galena shales at St. Paul and near Cannon 

 Falls, Minnesota. Also at Decorah, Iowa. A similar, perhaps identical, species occurs in the Trenton 

 of central Kentucky. 



Mm. JSegr., Nos. 7613, 8063. 



Batostoma winchelli Ulrich. 



PLATE XXVI, FIGS. 33-37; PLATE XXVII, FIGS. 1-6. 



Amplexopora winchelli Ulrich, 1SS6. Fourteenth Ann. Rep. Geol. Nat. Hist. Sur. Minn., p. 91. 



Zoarium irregularly ramose; branches subcylindrical or a little compressed, 

 varying in diameter from 4 to 10 mm., but in nine-tenths of the fragments seen from 

 5 to 7 mm. In the typical and common form of the species monticules are wanting, 

 nor are the clusters of apertures of larger size than the average, which sometimes 

 take their place, ever a conspicuous feature. Occasionally they are rendered more 

 distinct than usual by a thickening of the interspaces and an aggregation of the 

 mesopores. In a variety that may be distinguished as nodosa, the surface is thrown 

 up into more or less strongly marked monticules. Zooecial apertures rounded 

 or subangular, rather irregularly arranged,. ten to twelve in 3 mm.; walls moderately 

 thick in most specimens, comparatively thin in young, very thick in worn old ones, 

 ridge-shaped when perfect, and with acanthopore spines at nearly all angles of 

 i unction. Mesopores sparingly developed, never as numerous as the zocecia, occur- 

 ring chiefly in small straggling clusters, their mouths open, of various sizes, some of 

 them apparently developing into zooecia. 



