or 
BRYOZOA. 26 
Eridotrpya.] 
genus will include beside the following, probably two as yet undescribed species 
from the Trenton of Kentucky, Batostomella simulatriz Ulrich, a widely distributed 
species from the upper beds of the Hudson River group, Trematopora echinata Hall, 
from the Niagara group of Indiana, 7. ? (T’rematella ?) corticosa Hall (see Pal. N. Y., 
vol. vi, p. 15, pl. X, figs. 1-10), from the Lower Helderberg of New York, and Batosto- 
mella obliqua Ulrich, from the Hamilton group of Michigan. 
The systematic position of the genus, though in a measure doubtful, is probably 
intermediate between Homotrypa (compare H. similis Foord) of the Monticuliporide, 
and Bythopora, Miller and Dyer, of the Batostomellide. Because of the absence of 
cystiphragms it will be best to embrace the genus provisionally in the latter family. 
ERIDOTRYPA MUTABILIS, 2. Sp. 
PLATE XXVI, FIGS. 20-32. 
Zoarium ramose, dividing at rather long but irregular intervals ; branches 2 to 
6 mm. in diameter, the younger examples slender and nearly cylindrical, the old 
ones more or less irregular. Considerably over half of the hundreds of specimens 
seen are from 3.5 to 4.5 mm. in diameter. Zocecial apertures variable, the changes 
due chiefly to age, always oblique, the degree decreasing with age; walls thick, 
generally ridge-shaped and highest posteriorly, sloping gradually down into the 
apertures. In young examples—also in old ones on which a new layer of zocecial 
tubes was formed—the apertures may be exceedingly oblique and drawn out 
anteriorly. With age they became gradually more direct. The arrangement of the 
apertures is always more or less irregular, some of the short rows having six, others 
seven, and occasionally eight in 2mm. Small macule, either pitted or irregularly 
sculptured, commonly present in the older examples. In others the macule are 
represented by clusters of zocecia which, though a little larger than the average, are 
distinguished from them chiefly by the greater thickness of the interspaces. The 
mesopores too are most variable. In some cases, but this is rare, they will appear to 
be wanting over large portions of the surface (see fig. 24); in others they may be 
twice aS numerous as the zocecia. As a rule, however, they are to be counted as 
few, appearing at the surface, except in rare instances, only as occasional shallow 
depressions between the zoccial apertures. True acanthopores probably wanting, 
but small knots at the angles of junction may be noticed. 
Internal characters: These are, luckily, fairly constant in all essential features, 
the principal variations observed being in the number of mesopores. Figs. 26 to 28 
represent parts of sections prepared from an average example. Diaphragms occur 
