262 



THE PALEONTOLOGY OF MINNESOTA. 



IMesotrypa (?) rotunda. 



MESOTRYPA (?) ROTUNDA, n. sp. 



FIG. 17. Mesotrypa rotunda Ulrich, upper beds of the Galena shales, Hader, Goodhue county, Min- 

 nesota. Collection of E. O. Ulrich. 1, tangential section showing arrangement of cells about one of the 

 clusters. The latter embraces several young zooecia. 2, another portion of same section, with half of a 

 cluster shown above. 3, vertical section passing through a cluster like the one represented in 1, and 

 showing at center of figure several mesopores that have enlarged and assumed the tabulation of zocecial 

 tubes. 4, another portion of same section showing a partial break in the continuity of the tubes, and 

 consequent irregularities in their tabulation. All x 18. 



Zoariutn a small hemispheric mass, 10 mm. in diameter, 6 mm. high, and 4 mm. 

 thick at the middle, the under surface being strongly concave and wrinkled concen- 

 trically. Upper surface without monticules, but exhibiting fairly distinct clusters 

 of large cells, i - endered in many cases more so by aggregations of mesopores. Zoce- 

 cial apertures rounded, about eleven of the average size in 3 mm. Mesopores 

 abundant, but seeming never to separate the zooecia completely. Acanthopores 

 wanting. 



Internal structure as shown in the accompanying figures. 



This form is distinguished from the other species of the genus in having all the 

 diaphragms essentially horizontal. This fact casts some doubt upon the propriety of 

 placing the species under Mesotrypa, and the uncertainty of the reference is empha- 

 sized by undoubted relations with species now classed as Diplotrypa (e. g. D. milleri 

 Ulrich, and D. ? dubia Ulrich), having a decided leaning toward Callopora. 



formation and locality. Lower beds of the Galena limestone at Hader, Goodhue county, Minnesota. 



