PLATE LIIIYIIL 
Orthoceras Atreus. 
Page 305. 
See Plate 89. 
Fig. 1. A portion of an individual, preserving a large part of the chamber of habitation and nine air-cham¬ 
bers, showing the cylindrical chamber of habitation, with its constriction and the contraction of 
the tube at the aperture. The specimen is considerably compressed. Several branching, 
tubular furrows of a terebrous animal are shown traversing portions of the tube. Portage 
group. Rogers' Bridge, on the Genesee River below Portageville, N. Y. 
Orthoceras Thyestes. 
Page 306. 
Fig. 2. A much compressed and broken specimen, showing a poi’tion of the chamber of habitation and 
twenty-four attached air-chambers. The comparative depth of the air-chambers in this 
species and 0. Atreus, and the more rapid enlargement of the tube, is clearly shown in the 
figures. Several Cranice are attached to the chamber of habitation The ventral valves of 
two individuals are shown as merely a thickened rim. Three dorsal valves are represented, 
showing a subcentral apex, an4 concentric lamellose lines of growth. This species is here 
designated as Crania centralis. 
