PLATE XXIII 
Fig. 1. Endoceras proteiforme Hall. A, vertical section, showing the 
upper part of an endocone. B, cross-section showing siphuncle and endocone. 
Same specimen as fig. 3 on pi. XXI. 
Fig. 2. Endoceras proteiforme Hall. Vertical section through the siph- 
uncle, showing the apical part of an endocone. Same specimen as fig. 2 
on pi. XXI, and fig. 2 on pi. XXII. 
Fig. 3. Endoceras proteiforme Hall. Vertical section of the endocone 
in fig. le of pi. 49 of the Pal. of New York, vol. 1, 1847, to show its rate 
of taper and its form before it was distorted. See also fig. 2, on pi. XXV, 
and fig. 3 on pi. XXII. 
All specimens figured on this plate are from Middleville, New York, in the 
Trenton limestone. 
