240 ‘THE PALEONTOLOGY OF MINNESOTA. 
[Homotrypa tuberculata. 
their diameter ; that in the peripheral region the walls are moderately thickened, 
and the tubes occupied by a gradually crowding series of cystiphragms. The varying 
appearances of tangential sections are sufficiently exhibited in figs. 22 to 25. The 
differences so far observed in these sections consist almost entirely of variations in 
the number and size of the acanthopores. 
(ireatly increased collections, and the study of numerous sets of thin sections, 
have convinced me of the specific identity of H. swbramosa and H. insignis. The 
latter name might be retained in a subordinate sense for the Galena shales variety, 
in which the clusters of large cells are more conspicuous, the average size of 
the zoarium smaller, the zocecial walls thinner, and the acanthopores permanently 
less numerous and smaller than in the typical middle and upper Trenton shales 
form of the species. 
The tabulated axial region, more numerous and larger cystiphragms, the 
presence of acanthpores, and the irregular and more compact growth, will distin- 
guish the species from preceding forms of Homotrypa. Thin sections will of course 
separate it at once from outwardly more similar species, belonging to other genera, 
that are associated in the same beds. 
Formation and locality.—H. subramosa is rare in the middle third of the Trenton shales at several 
localities in St. Paul and Minneapolis, but is much more abundant in the upper third of the shales at St. 
Paul and localities in Goodhue county, Minnesota. The restricted var. insignis is comparatively rare in 
the Galena shales at localities in Goodhue and Fillmore counties; also in the same beds at St. Paul, and 
at Decorah, Iowa. 
Mus. Reg, Nos. 5977 to 5980, 8030, 8061. 
Homotrypa TUBERCULATA, 7%. Sp. 
Fia. 14 Homotrypa tuberculata, n. sp., upperathird Trenton shales, near Cannon Falls, Minnesota. 
Collection of BE. O. Ulrich. a, fragment-of the natural size; b, small portion of a vertical section, x 18, 
showing two mesopores, the cystiphragms and diaphragms of the peripheral region, all of which are want- 
ng in the axial region; ec and d, two portions of a tangential section of a fully matured example, x 18, the 
former showing appearance immediately beneath the surface, the latter at a slightly deeper level. 
