230 THE PALEONTOLOGY OF MINNESOTA. 



[Homotrypella multiporata. 



mesopores and acanthopores developed. The mesopores are distinguished .from the 

 zocecia by their shortness and in having no cystiphragms. The latter structures 

 numbiBr from three or four to fifteen in a direct series in each zooecial tube. In 

 most cases they occur only in the region intervening between the fully matured 

 peripheral and the immature axial region. Beyond them the diaphragms are crowded 

 and essentially horizontal. In the mesopores the diaphragms are often thick and 

 situated about the same distances apart as in the zooecial tubes, with from fourteen 

 to seventeen in 1 mm. In the axial region of transverse sections the zooecial tubes 

 are of unequal sizes and of peculiarly irregular shapes. 



Formation and locality.— B.a.theT abudant in the middle third of the Trenton shales, at St. Paul. 

 Minneapolis, Cannon Falls, near Fountain, and other localities in Minnesota. 



Mus. Beg. Nos. 5025, 5981, 5982. 



Homotrypella multiporata, n. sp. 



PLATE XVIII, PIGS. 21, 22. 



Zoarium ramose, branches cylindrical, 8 or more mm. in diameter. Zooecia 

 small, about twelve in 3 mm., with thin walls, rounded or petaloid apertures, their 

 margins raised slightly and separated by a conplete ring of small mesopores. Acan- 

 thopores small, numerous. Cystiphragms seen only m the turn of the zooecial tubes, 

 as far as observed, varying between two and six in each tube. Diaphragms in zooecial 

 tubes exceedingly delicate, five or six in 1 mm.; a little stronger in the mesopores, 

 and here numbering about nine in each tube ; apparently wanting in the axial region, 

 where the tube walls are minutely crenulate and thin. In the axial region of trans- 

 verse sections the tubes are very unequal. 



This species, so far as observed, forms thicker branches, has much more numer- 

 ous mesopores, and smaller and thinner-walled zooecia than its associate H. instabilis. 

 Internally the diaphragms are wider apart in both sets of tubes and more delicate. 

 They diflfer again in being twice as numerous in the mesopores as in the zooecial 

 tubes. None of the other species are sufficiently related to require comparisons. 



Formation and locality.— Raxe. in the middle third of the Trenton shales, at St. Paul and Minne- 

 apolis, Minnesota. 



HOMOTRPELLA (?) SUBGEACILIS, W. Sp. 

 PLATE XXVI, PIGS. 10-16. 



Zoarium . small, ramose, dividing irregularly; branches subcylindrical, 2 to 4.5 

 mm. in diameter ; surface without monticules and maculae. Zooecia rather irregular 

 in size, shape and arrangement, varying also in the thickness of their walls, these 

 being often stronger than shown in f^gs. 15 and 16, plate XXVI ; twelve or thirteen 



