MIDDLE CAMBRIAN. 
29 
In the form under consideration the coronal intestine is confined, so 
far as we know at present, to the simple, direct, radial canals extending 
from the central disk to the margin of each exumbrella 
and interumbrella lobe. These canals are large in pro- 
portion to the size of the lobes (see PL. II, figs. 6 and 7; 
Pl. III, figs. 3 and 4; Pl. IV, figs. 7, 8, 9, 10a, 11a, 13) 
and are not branched. There is no trace of a connect- 
ing coronal intestine, and it is probable that the canals 
terminated in a minute excreting opening at the margin 
of the exumbrella, as similar canals do in Aurelia, 
although in the latter a coronal canal exists. 
Genitalia —No traces of the reproductive system have 
been observed. 
Oral opening, plate, and arms.—No traces of an oral opening 
have been seen. In a number of specimens, where the 
oral plate and arms have been re- 
moved prior to the fossilization of 
the animal, a circular depression is 
Fic. 5.—Brooksella alterna- 
ta. Diagrammatic central 
vertical section through the 
central axis between the radi- 
ating lobes. 
The description of the let- 
tering is to be found under 
tert fig. 4 (p. 28), with the ex- 
ception of that of the letter /, 
which refers to that portion of 
the umbrella between the free 
lobes and exterior to the pil- 
lar canals. 
Fic. 6.—Brooksella alternata. 
Diagrammatic vertical section 
after figs. 4, 4a,4b of Pl. I, so as 
to cut between the subumbrella 
lobes. Interior restored. 
a, exumbrella lobes, with ra- 
dial canals; b, interlobe, with 
interior canal; k, axial or pillar 
canals; 0, oral arm, with inte- 
rior canal; z, central axis. 
before one was found in which they were preserved, 
and this specimen is thus far unique (Pl. I, figs. 8, 
The medusa was crushed obliquely down 
and the exumbrella lobes turned inward, the oral plate 
and arms being pushed to one side of the center. 
The oral plate is formed by the union of the four 
arms at the center (PI. II, figs. 8, 8a). 
is broken off about 1™ from the center; the sections 
tions have an average diameter of 5™" by a depth of 7™*; 
8a, 8b). 
seen at the base of the central axis (PI. I, fig. 3a, a’). 
This was probably the location of the mouth at an 
early stage in the evolution of this species and the 
development of the individual, but with the develop- 
ment of the oral plate and arms it was covered over. 
The presence of a typical oral 
plate and arms was for a long 
time in doubt; upwards of 1,500 
specimens had been collected 
Fig. 7.—Brooksella alternata. 
Diagrammatic vertical median 
section of same specimen as text 
fig. 6, soas to cut through the sub- 
umbrella and exumbrella iobes 
and the central axis. The radial 
canals and central stomach (or in- 
testinal tube) are drawn in from 
information partly obtained from 
Each arm other specimens. 
of the terminal por- 
the opening of 
