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 
number from three or four to fifteen in a direct series in each zocecial 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 zocecial tubes, with from fourteen 
to seventeen in | mm. In the axial region of transverse sections the zocecial tubes 
are of unequal sizes and of peculiarly irregular shapes. 
Formation and locality.x—Rather abudant in the middle third of the Trenton shales, at St. Paul. 
Minneapolis, Cannon Falls, near Fountain, and other localities in Minnesota. 
Mus. Reg. Nos. 5025, 5981, 5982. 
HomotTryPELLA MULTIPORATA, #. Sp. 
PLATE XVIII, FIGS. 21, 22. 
Zoarium ramose, branches cylindrical, 8 or more mm. in diameter. Zocecia 
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 in the turn of the zocecial tubes, 
as far as observed, varying between two and six in each tube. Diaphragms in zocecial 
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 zocecia than its associate H. instabilis. 
Internally the diaphragms are wider apart in both sets of tubes and more delicate. 
They differ again in being twice as numerous in the mesopores as in the zocecial 
tubes. None of the other species are sufficiently related to require comparisons. 
Formation and locality.—Rare in the middle third of the Trenton shales, at St. Paul and Minne- 
apolis, Minnesota. ; 
HoMoTRPELLA (?) SUBGRACILIS, ”. Sp. 
PLATE XXVI, FIGS. 10-16. 
Zoarium small, ramose, dividing irregularly; branches subcylindrical, 2 to 4.5 
mm, in diameter ; surface without monticules and macule. Zocecia rather irregular ° 
in size, Shape and arrangement, varying also in the thickness of their walls, these 
being often stronger than shown in figs, 15 and 16, plate XX VI; twelve or thirteen 
