PAs hS Tit: 
BROOKSELLA ALTERNATA (p. 23). 
Fic. 1. Outline of an exumbrella, the central portion of which has been worn away so as to expose 
the radial canals (x, v, x), and the central cavity at a. 
Fic. la. View of the flattened subumbrella surface of fig. 1, showing the narrow lobes and 2 inter- 
radial arms. 
Fic. 2. Outline of the subumbrella surface of a compressed individual in which the openings of the 
radial canals of the exumbrella are unusually large. 
Fic. 3. View of a worn specimen showing the radial canals of the exumbrella lobes. 
Fia. 4. Specimen showing the radial canals and central cavity even more distinctly than in figs. 1 
and 3. 
Fic. 5. Side view of a broken specimen resting on the ventral surface, showing sections of the 
umbrella and interradial lobes. 
Fic. 6. View of the subumbrella of a very narrow-lobed individual. Sections of the lobe are shown 
at x, x. 
Fig. 7. A 7-lobed individual resting upon an individual having 12 or more lobes, 
Fic. 8. Specimen dissected by weathering so as to show some of the interradial arms united to the 
central axis, the extension of the upper lobes being shown at x, wv, xv, x. 
Fic. 9. A crushed specimen that may belong to this species. 
Fia. 10. A specimen preserving what appears to be an unusual form of an exumbrella lobe (a). It 
resembles one of the interradial lobes. 
BROOKSELLA CONFUSA (p. 30). 
Fic. 11. Subumbrella surface of a specimen the exumbrella of which is much like that of fig. 3 of 
Pl.I. The relations of the various lobes are shown in the figure, and the free interradial 
or oral lobes at x, a, a. 
Fias. 12, 12a. View of the exumbrella and several of the interradial lobes. The relations of the 
two sets of lobes are shown in the side view, fig. 12. 
Fia. 12b. Subumbrella surface of fig. 12, showing essentially the same arrangement as fig. 11. 
Fic. 13. Subumbrella view of an individual in which the interradial lobes are numerous and the 
subumbrella lobes somewhat more regular than in figs. 11 and 12b. 
110 
