264 THE PALEONTOLOGY OF MINNESOTA. 
[Bythopora alcicornis. 
The species is closely related to B. arctipora Nicholson, sp., of the Cincinnati 
rocks, but the zocecial apertures are narrower and more produced anteriorly than in 
that species. 
Formation and locality.—Fragments of this species are common in the middle third of the Trenton 
shales at St. Paul and Minneapolis, Minnesota. Good specimens, however, are rare. 
Mus. Reg. Nos. 6012, 6013. 
ByTHOPORA ALCICORNIS, 7. Sp. 
PLATE XXVI, FIGS. 7-9. 
In this species the zoarium divides at shorter intervals than in any other of the 
genus known, the distance between the branches varying between the extremes of 1.5 
to 6.0mm. Compared with B. herricki, we find that the average size of the branches 
is a little less, that they bifurecate at shorter intervals, that the zocecial apertures are 
arranged less regularly and on the whole less compactly, the direction of the rows 
being interrupted and changed by meeting with spots, 2 or 8 mm. apart, in which 
the interspaces between the apertures are much wider than elsewhere. These sub- 
solid spots distinguish the species from all the others as well, excepting an unde- 
scribed larger form occurring in the upper beds of the Hudson River group at 
Waynesville, Ohio, in which they are of greater extent and constitute a very obvious 
superficial character. 
Formation and locality.—Upper third of the Trenton shales, associated with Phylloporina corticosa 
and Prasopora conoidea, near Cannon Falls, Minnesota. 
Genus ERIDOTRYPA, n. gen. 
Batostomella (part.) ULrrcn, 1890. Ill. Geol. Sur., vol. viii, pp. 375, 432. 
Zoaria ramose, branches slender. Zocecia more or less oblique, with thick walls, 
the tubes intersected by diaphragms only. The latter may be wanting in the axial 
region, are in most cases absent for a short distance within the apertural edge, but 
always present and closest together in the turn from the axial into the narrow 
peripheral region. Mesopores with close-set diaphragms, varying in number, some- 
times abundant, at other times very few. Acanthopores small, never numerous, 
sometimes wanting. 
Type: Hridotrypa mutabilis, n. sp. 
This genus became necessary partly through the restriction of Batostomella to 
its Carboniferous types, and partly for the accommodation of a number of species 
that could not be disposed of satisfactorily under any of the existing genera.* The 
*It is unfortunate that both Hall’s recently proposed Trematella (Pal. N. Y., vol. vi, p. xiv, 1887) and my Batostomella (1882) 
should have been founded upon practically the same type of structure. In both cases species are included doubtfully that 
are now to go under Eridotrypa. 
