234 THE PALEONTOLOGY OF MINNESOTA. 
[Homotrypella rustica. 
HomoTRYPELLA RUSTICA, ”. Sp. 
PLATE XVIII, FIGS. 31-33. 
Zoarium irregularly ramose, branches 5 to 10 mm. in diameter. Low swellings 
of the surface, scarcely to be called monticules, occasionally present. Surface very 
rough under a hand lens, the acanthopores being strong and numerous, though not 
materially inflecting the zocecial walls. Zocecial apertures rounded, about eleven in 
3mm. Mesopores abundant, though but rarely separating the zocecia completely, 
of unequal sizes, rounded at the surface. 
Internal characters: In tangential sections, showing the characters immediately 
beneath the surface, (upper part fig. 32) the zocecia are rounded, with only moder- 
ately thick walls, the mesopores sharply defined, subangular, of unequal sizes, and 
averaging three or four to each zocecium, the acanthopores strong, perhaps two to 
each zocecium, and situated chieflly in the zocecial walls, which they occasionally 
only cause to bend inwardly. At a deeper level (lower part fig. 32) the walls are 
thinner, the acanthopores smaller, and the mesopores larger. At both levels the 
zocecia almost uniformly exhibit the cut edges of cystiphragms. In vertical sections 
the most striking feature of the species is the abundant tabulation of all the tubes. 
Diaphragms occur all through the axial region, and both the mesopores and acantho- 
pores began earlier than usual. The outward curving of the tubes also is unusually 
gradual. The diaphragms in the two sets of tubes are subequally distributed, and 
it is often difficult to discriminate between them when the curved edges of the 
cystiphragms are not shown. At about the middle of the curve nine or ten dia- 
phragms occur in 1 mm.; nearer the surface they are a little closer, while more toward 
the center of the branch they are further apart. The cystiphragms are unusually 
superficial in this species, forming crowded series almost to the mouths of the 
zocecia. 
This species is distinguished from H. granulifera and H. mundula by the greater 
number and open character of the mesopores; from H. multiporata by its larger 
zocecia, fewer and more unequal mesopores, and more crowded as well as different 
tabulation of the tubes. H. instabilis has thicker walls, and is quite different in other 
respects. 
Formation and locality.—The sections illustrated were prepared from a single example collected by 
the author in the upper beds of the Hudson River group, at Spring Valley, Minnesota. This specimen 
seems identical with a common species occurring at an equivalent horizon in Indiana and Ohio, to which 
I had applied the name rustica in my MS. notes. 
Mus. Reg. No. 8125. 
