BRYOZOA. 259 
Mesotrypa (?) spinosa.] 
The mesopores are less numerous, and the tabulation of both sets of tubes more 
crowded than in M. whiteavesi Nicholson, sp. In M. regularis Foord, sp., the dia- 
phragms are few in the zocecial tubes. This is likewise true of M. quebecensis Ami, sp., 
in which acanthopores seem to be wanting entirely. 
Formation and locality.—In the middle third of the Trenton shales at Minneapolis, St. Paul and 
localities in Goodhue and Fillmore counties, Minnesota. 
Mus. Reg. No. 5993. 
MesorryPa (?) SPINOSA, 2. Sp. 
PLATE XVII, FIGS. 9-12. 
Aspidopora parasitica (part.) ULRICH, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Sur. Minn., p. 90. 
Zoarium parasitic, 0.5 to 6.0 mm. thick. Zocecia small, circular, neatly arranged 
about the clusters, twelve or thirteen of the ordinary size in 3mm. Interspaces or 
walls rather thick, but the abundant mesopores shown in thin sections are rarely, if 
ever, to be made out at the surface. This may be due in part to the large size and 
prominence of the acanthopores. Internally, with crowded horizontal diaphragms in 
the mesopores and mostly oblique curved partitions in the zocecial tubes. Sometimes 
a few at the bottom of the tubes are precisely like ordinary cystiphragms (fig. 12). 
This form seems to hold an intermediate position between M. infida and Aspi- 
dopora parasitica, differing from the first in having smaller zocecia, thicker walls and 
stronger acanthopores, and from the second in the greater thickness of the zoarium, 
much stronger acanthopores, different tabulation of the zocecial tubes, and in but 
rarely showing the mesopores at the surface, these being, so far as observed, always 
distinctly visible at the surface of A. parasitica. Atactoporella insueta, another asso- 
ciated parasitic species, has larger and less regularly distributed zocecia, with smaller 
and more numerous acanthopores. 
Formation and locality.—Perhaps the commonest of the parasitic Bryozoa occurring in the middle 
third of the Trenton shales at St. Paul, Minneapolis and other localities in Minnesota. 
Mus. Reg. No. 8127. 
MESOTRYPA QUEBECENSIS Ami, sp. 
FIG, 15, e and f, PAGE 248. 
Diplotrypa quebecensis Ami, 1892. Canadian Record of Science, p. 101. 
Zoarium discoid or subhemispheric, base gently concave, hight 4 to 20 mm., 
diameter 12 to 45 mm. At Decorah, Iowa, the specimens are generally about 25 
mm, in diameter, and. 6 or 7 mm. thick. The same is true of the Kentucky 
examples, but in New York and Canada they are usually nearly again as large. 
