294 THE PALEONTOLOGY OF MINNESOTA. 
(Batostoma humile. 
occasionally appearing subsolid. Acanthopores numerous, rather small, often indent- 
’ ing the zocecial apertures. Interspaces variable, occupied by closed mesopores, often 
thinner and the zocecial 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. 
6 
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, ”. 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 spimulose in the older stages. Zoccial 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 zoccial apertures 0.15 by 0.2 mm. against 0.2 by 0.8 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 zowcia, With age the walls become thickened, ring-like and 
