PLATE I . 



Brooksella alternata (p. 23). 



Fig. 1. View of an exumbrella with 6 lobes and a depression over the central stomach. 



Fig. 2. An exumbrella with 8 lobes and with a much larger central depression than that of fig. 1. 



Fig. 3. An exumbrella with 9 lobes and preserving a trace of the corona furrow in the ring about 

 the central disk. 



Fig. 3a. View of the under or subumbrella side of fig. 3. The narrow subumbrella lobes are well 

 shown, and also what appear to be oral arms, x, x. These oral arms appear to be of the 

 same type as those of Laotira cambria, as shown by figs, la, 2, and 3c of PI. XVIII. A 

 slight circular depression at the center (,r) may possibly indicate the position of the 

 primitive oral aperture, or the depression beneath the buccal stomach. 



Fig. 4. Exumbrella view of an unusually rotund specimen. A projecting interradial lobe or arm is 

 shown at x. 



Fig. 4a. Subumbrella view of fig. 4. An interradial lobe or arm is shown at x, and a broken subum- 

 brella lobe at b. The lobe at a apparently did not connect with the exumbrella. It 

 appears to have been an interumbrella lobe or arm that was attached at the same gen- 

 eral plane as the subumbrella lobes. 



Fig. 4b. Side view of fig. 4, showing the lobes described in figs. 4 and 4a. 



Fig. 5. View of an exumbrella with 5 lobes which are continued into the subumbrella lobes. 



Fig. 5a. Side view of the same. 



Fig. 6. An exumbrella with 7 main lobes and 2 smaller ones (x,x). The lobes are much narrower 

 than those of figs. 1 and 5, and their lower portion has been worn away so as to expose 

 the radial canals that extend from the central disk through each of the exumbrella lobes. 



Fig. 7. An exumbrella with 8 narrow lobes and 4 smaller interumbrella lobes (.»', x, x, x). 



Fig. 8. An exumbrella showing lobes of various width and several interumbrella lobes (x, x, x). 



Fig. 8a. View of the subumbrella of fig. 8. The lower sides of the interumbrella lobes of fig. 8 are 

 indicated by ,r. x, x. The exumbrella lobes proper («, a, a) merge into the 5 narrow 

 subumbrella lobes which meet at the center. 



Fig. 9. An exumbrella in which the interumbrella lobes are a much more prominent feature than 

 in fig. 8. The specimen appears as though an individual was resting upon and clasping 

 one beneath. The exumbrella lobes (a to/) . however, merge into the subumbrella lobes 

 « to / of fig. 9a. 



Fig. 9a. View of the subumbrella of fig. 9. 



lU(i 



