238 



THE PALEONTOLOGY OF MINNESOTA. 



HOMOTRYPA (?) INTERCALARIS, tt. Sp. 



b 



tHomotrvpa (71 intercalarls . 



;;% . ;* 

 SSvi &; 



FIG. 13. Homotrypa (?) intercalaris, n. sp., middle Trenton shales, Minneapolis, Minnesota. Collec- 

 tion of E. O. Ulrich. a and b, a specimen of the natural size, and small portion of its surface x!8, showing 

 unusually oblique zowcial apertures; c and d, similar views of a fragment of a form doubtfully referred to 

 this species, having somewhat smaller zocecia and mural papilla 1 ; e and /, similar views of a typical 

 example; g, more slender fragment, natural size; h, tangential section, x!8, showing structure immediately 

 beneath surface of fully matured example; i, another portion of same section, showing structure at a deeper 

 level; j, vertical section, x!8, showing the peripheral region with the mesopores and cystiphragms, and a 

 small part of the untabulated axial region. 



Zoarium small, ramose, branches subcylindrical, generally 2.5 to 3.5 mm. in 

 diameter. Surface without monticules but exhibiting distinct clusters of large cells 

 in the centers of which there is often a small aggregation of mesopores. Zooecial 

 apertures rounded or subangular, commonly direct to the surface, at other times 

 more or less oblique, occasionally so much so (see fig. 13 b) that they recall those of 

 Ceramoporella. The last condition probably occurred only when a new layer of zooecial 

 tubes was developed in which the individual cells failed to correspond exactly with 

 those ot preceding layers. Typical form with about thirteen zocecia in 3 mm.; the 

 variety, also figured above, has fifteen in the same distance. Walls or interspaces 

 of moderate thickness, commonly with very few and inconspicuous acanthopores. 

 But in the variety a row of minute papillae has been observed along the center of 

 the wall. Mesopores rather abundant, occurring at most of the angles of junction 

 between the zooecia. 



The internal structure is brought out sufficiently in the accompanying cut. 

 Figures h and i show how very similar tangential sections may be to those of the 



