294 THE PALEONTOLOGY OF MINNESOTA. 



IBatostoma humllc. 



occasionally appearing subsolid. Acanthopores numerous, rather small, often indent- 

 ing the zooecial apertures. Interspaces variable, occupied by closed mesopores, often 

 thinner and the zooecial walls more in contact with each other than shown in fig. 27. 

 About ten zocecial apertures in 3 mm. 



None of the specimens at hand have preserved the internal characters in a fully 

 satisfactory manner. The sections prepared, however, are sufficiently clear to make 

 the generic reference of the species unquestionable. They point, furthermore, to 

 close relationship with B. varium, differing from that species in having the periph- 

 eral region narrower and diaphragms less abundant. Of external peculiarities the 

 possession of well marked monticules distinguishes the species from all related 







forms. For comparisons with associated monticulose species belonging to other 

 genera see p. 227. 



Formation and locality. Not uncommon in the upper third of the Trenton shales at Poe's farm, 

 near Cannon Falls, Minnesota. 



Mus. Reg. No. 8134. 



BATOSTOMA HUMILE, n. sp. 



PLATE XXV, FIGS. 29-36. 



Zoarium rather small, consisting of comparatively slender, compressed or sub- 

 cylindrical branches, 4 to 11 mm., commonly 5 to 7 mm., in width; bifurcations few, 

 less frequent than usual with species of this genus; surface without monticules, but 

 more or less strongly spinulose in the older stages. Zocecial apertures subovate, 

 varying in size according to thickness of walls and interspaces, generally with a 

 thickened rim; apertures subequal, eight or nine in 3 mm. Interspaces variable, 

 depressed, the zocecial walls sometimes in contact at as many points as the rounded 

 form of the tubes will admit; more commonly their walls are completely separated. 

 At intervals the interspaces may widen and form subsolid spots. Acanthopores 

 numerous, situated in the interspaces or on the outer side of the walls, small and 

 often difficult to distinguish on young examples, but conspicuous enough on well 

 matured specimens and very much so on several apparently old fragments. In the 

 latter the interspaces may be solidified and raised instead of depressed, and the 

 size of the zocecial apertures 0.15 by 0.2 mm. against 0.2 by 0.3 mm. in young 

 specimens. 



Internal characters: Good tangential sections cannot be prepared except from 

 fully matured or old examples, because of the brevity of the peripheral region. 

 Young specimens give tangential sections like the upper half of fig. 33, with thin 

 walls and angular zooacia, With age the walls become thickened, ring-like and 



