PLATE CXX. 
Gomphoceras eximium. 
Page 32. 
, See Plate 121. 
Fig. 1. An outline representing the size and foi’m of a large individual, showing the point of greatest 
gibbosity and the frequency of the septa. 
Fig. 2. Longitudinal section of a fragment showing the nummuloid siphuncle and the septa. Many of 
the septa have been removed by the process of maceration before being imbedded, and the 
course of the siphuncle toward the apex is indicated by a discoloration of the filling of the air- 
chambers. In the upper porlion of the siphuncle, at the extremities of the cusps where the 
tube penetrates the septa, are seen several indications of an organic deposit, or a thickening of 
the walls of the siphuncle. 
Fig. 3. Id. The end of the siphuncle showing the radiate api^earance of the deposit mentioned under the 
preceding figure. 
Upper Helderberg limestone. Cohmnbus, Ohio. 
Gomphoceras impar. 
Page 32. 
See Plate 121 a. 
Fig. 4. View of the specimen desci-ibed, preserving the chamber of habitation and a portion of seventeen 
air-chambers. Tlie tube shows three constrictions or undulations which apparently represent a 
normal condition of growth. 
Upper Helderberg limestone. Columbm, Ohio. 
Gomphoceras nasutum. 
Page 34. 
See Plate 121. 
Fig. 5. Ventral view, showing the form of the chamber of habitation, and the sinus and reflection of the 
margin, forming the small aperture. Traces of the crenulated zone are shown at the base of 
the grand chamber whei'e the tube suddenly contracts forming a shoulder at its junction with 
the septate portion. 
Fig. 6. Id. View of the aperture, showing its broad elliptical form and the sinus in the margin corres¬ 
ponding to the ventral or small aperture. 
Fig. 7. Id. Transverse section representing the position and size of the siphuncle. 
Chemung group. Belmont, Allegany coujity, N. T. • 
