BRYOZOA. 257 
esotrypa.] 
Internal characters: These are sufficiently illustrated on plate XVII, but it is well 
to state that a few tubes in both vertical and tangential sections may show a single 
cystiphragm at the bottom. Diaphragms are wanting, as are acanthopores also. 
This beautiful bryozoan is a true Aspidopora, and is rather closely related to 
A. newberryi Nicholson, sp., the only reliable or constant difference between them 
being in the number of cystiphragms. In the present species these structures are so 
few that they may appear to be wanting entirely, but in Nicholson’s species they 
occur in every zocecial tube, numbering in each, according to age, from one to ten. 
Several discoidal forms are to be found in che same beds with A. elegantula, but none 
of them are sufficiently like it to render confusion probable. 
Formation and locality.—Rather rare in the Galena shales at St. Paul, and near Kenyon, Goodhue 
county, Minnesota. 
Mus. Reg. No. 8126. 
Genus MESOTRYPA, n. gen. 
Diplotrypa (part.) NIcHOLSON, 1879, Pal. Tab. Cor., p. 312, and 1881. The Gen. Monticulipora, pp. 101 
and 155, 
Zoaria hemispheric, conical, or discoidal, generally free, with the lower surface 
covered by an epitheca. Zocecial tubes prismatic or cylindrical, more or less sep- 
arated from each other by angular mesopores; internally with oblique and some- 
times funnel-shaped diaphragms, that often simulate and probably are to be regarded 
as peculiarly modified cystiphragms. Mesopores becoming smaller with age, inter- 
sected by numerous diaphragms. Acanthopores generally present, sometimes of 
large size. ‘ 
Type: Diplotrypa infida Ulrich. 
This genus is established for a natural group of species heretofore referred, 
erroneously, I believe, to Diplotrypa*. These species are D. regularis Foord, D. que- 
becencis Ami, D. whiteavesi Nicholson, D. patella Ulrich, the type D. infida, and three 
new species, M. discoidea, M. rotunda, and M.(?) spinosa. To these might be added the 
Niagara D. milleri Ulrich, but as the position of that species is somewhat in doubt, 
it had best be left as originally placed till an opportunity offers to rework the type 
specimens. 
The affinities of the proposed genus are not with Diplotrypa but with Prasopora. 
Indeed, for some time I considered the propriety of referring the group to Prasopora, 
yet after mature reflection the erection of a new genus was decided upon as serving 
the purposes of classification better than would have been done by extending the 
limits of that genus. 
*See part ii, Contri. Micro-Pal, Cambro-Sil. Rocks, Can., p. 32, 1890. 
ee 
