980 The American Naturalist. [November, 
Gastropoda 
Pteropoda 
Crustacea. 
Trilobita . ‘ 
i : 13 species. 
i i : . 15 species. 
8 species. 
51 species. 
The astonishing number of 141 American species was there- 
fore known in 1890 from this very old series of rocks, and this 
has since been added to until there are now known from the 
world nearly 200 species, distributed among about 75 genera. 
The illustrations accompanying this article show some mem- 
bers of most of the classes above-mentioned. In Figure 4 is 
Fig. 4. Archeocyathus pro- 
fundus. 
shown the cup of a small specimen of 
Archæocyathus profundus, one of. the 
Actinozoa. In Figure 5 we have two 
views of Medusites lindstromii, one of the 
Hydrozoa, and supposed to represent 
casts of the gastric cavity of a jelly- 
fish. In Figure 6 there are shown a 
number of forms of Brachiopoda, a class 
which, in times past, was very abund- 
ant, but which now has only a limited 
number of representatives. Figure 7 shows some species of 
Fig. 5. Medusites lindstromit. 
Gastropods and Figure 8 the three known species of Lamelli- 
branchiata or bivalve shells which are, to-day, so abundant in 
the fresh and salt waters of the globe. In Figure 9 there is 
