BRYOZOA. 249 
Prasopora contigua. | 
Prasopora contiaua Ulrich. 
PLATE XVI, FIGS, 24-26 
Prasopora contigua ULRICH, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Sury. Minn., p. 87. 
Zoarium hemispheric, base flat or slightly concave, usually less than 30 mm. in 
diameter. Zocecia with very thin walls and polygonal apertures, ten or eleven of 
the average size in 8mm. Clusters of zocecia, some of them attaining a diameter 
of 0.87 mm., occur at intervals of a little less than 4 mm. Mesopores comparatively 
few, often difficult to detect at the surface. 
Internal structure: Tangential sections show that the zocecial walls are polygonal 
and very thin, with neighboring cells in contact, except at many of the angles of 
junction, these being occupied by one or two small mesopores. The latter often 
form very inconspicuous clusters at the center of the groups of large zocecia, but 
in the intermediate spaces not over half of the angles of junction between the 
ordinary zocecia are occupied by mesopores. A few very small acanthopores are 
developed. The opening left by the cystiphragms is generally of ovate form and 
more often eccentric than central in its position within the tube cavity. 
Vertical sections are peculiar chiefly because they exhibit a marked decrease in 
the number of mesopores when compared with other species of the genus. 
This form is closely related to P. simulatriz, and perhaps should be classed as a 
variety of that species. The distinguishing features are (1) the much smaller num- 
ber of mesopores, (2) thinner walls, (3) the presence of small acanthopores, and (4) a 
somewhat greater crowding of the cystiphragms, these averaging over twenty in 
2mm. More specimens are necessary before the constancy, and, therefore, value, of 
these differences can be established fully. The same species, very slightly modified, 
occurs at Cincinnati, Ohio, about three hundred feet above the Ohio river bed. 
Formation and locality—The Minnesota specimens are believed to have been found either in the 
upper part of the Trenton shales or in the Galena shales, at localities in Goodhue and Dakota counties. 
Mus. Reg. Nos. 5301, 5534, 5989. 
Prasopora conoipEA Ulrich. 
PLATE XVI, FIGS. 11-15. 
Prasopora conoidea ULRICH, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. Minn., p. 87. 
Zoarium generally depressed-conical, with the hight a little more than half the 
diameter ; at other times subhemispherical; hight varying from 4 to 16 mm., the 
diameter from 8 to 20 mm. Under surface rather deeply concave, wrinkled concen- 
trically, with a small central scar. Upper surface celluliferous and presenting, at 
