304 THE PALEONTOLOGY OF MINNESOTA. 
{(Monotrypa magna. 
The genus as restricted embraces but few species. Besides the type, which 
occurs in the Trenton of Canada and New York, we have M. subglobosa Ulrich, in 
the Utica horizon at Cincinnati, MW. rectimwralis Ulrich, in the Trenton of southern 
Illinois and probably in the Cincinnati group of Ohio, M. intabulata, n. sp., and M. 
(2 Chetetes) cumulata, n. sp., in the Galena of Minnesota, M. magna, n. sp., in the 
Birdseye limestone of the northwest, M. colliculata (Chetetes colliculatus Hall,) in the 
Lower Helderberg of New York, and M. tabulata (Ptychonema tabulatum Hall,) in the 
Upper Helderberg of New York. A small undescribed species occurs in the Niagara 
of Indiana, while another, apparently belonging here, I found in the Corniferous 
limestone at Columbus, Ohio. 
MonotTrypa MAGNA, 7, Sp. 
PLATE XXVII, FIGS. 28 and 29. 
Zoarium growing in large expanded masses, sometimes consisting of superposed 
layers, the whole perhaps 20 to 40 mm. high and 100 mm. wide; under side generally 
with a wrinkled epitheca, the upper celluliferous and without monticules, Zocecia 
large, polygonal, thin-walled, with clusters of larger size than the average at inter-. 
vals of about 6 mm., measuring from center to center; about nine in 5 mm.; size of 
largest in the clusters about 0.8 mm., average diameter of these in the spaces between 
the clusters about 0.5 mm. 2 
Internal characters: In vertical sections the zocecial walls are strongly undulat- 
ing and very thin throughout, and the tubes crossed by complete horizontal dia- 
phragms at intervals varying between one and three times the diameter of a tube. 
Transverse sections exhibit thin structureless walls, an occasional small (young) 
cell, and a total absence of mesopores and acanthopores. 
The larger size of the zocecia distinguishes the species from M. undulata Nichol- 
son. Excepting the Crepipora perampla of the present work, they are larger than in 
any paleozoic bryozoan known to me. The zoaria of that species are comparatively 
higher and less expanded, and their zocecia provided with lunaria. 
Formation and locality—Not uncommon in the ‘‘Lower Blue” limestone at Dixon, Dlinois; also 
at Mineral Point and Beloit in Wisconsin. A small fragment from the equivalent limestone at Minne- 
apolis is provisionally identifled with it. 
