198. A POPULAR EXPOSITION, OF THE 
(fig. 169), Maclurea Logani (fig. 170), Ormoceras (Orthoceras) tenus- 
filum (fig. 171), Ormoceras ((onioceras) anceps (fig. 172), and other 
orthoceratites with beaded siphuncle (see ante, Part IV.) Also species 
of Lituites, Cyrtoceras, and Phragmoceras (figs. 173, 174, and 175). 
Bie. 171.—Ormoceras Fig. 172.—Ormoceras Fig. *78.— Lituites undatus 
tenuifilum (Hall). anceps (Hall). (Hall). 
Fig. 174.— Cyrtoceras Fig. 175.— Phragmoceras Fig, 176.— Oncoceras 
annulatuin. prematurum (Billings). constricéum (Hall). 
The more characteristic or otherwise interesting fossils of the 
Upper or Trenton subdivision, properly so-called, are exhibited in 
the following figures. The zoological positions and affinities of these 
have already been indicated in Parr IV. 
Fig. 178. — Petraia 
cornicula (Hall). 
Fig. 177.— Sienopora fibrosa* Fic. 179.—Glantocystites 
(Goldruss). Logana (Billings). 
* he circular varieties of this coral are sometimes known as S, petropolitana, 
