CEPHALOPODA 329 



GOMPHOCERAS EXlMIUM. 

 PLATE XLIV, FIGS. 1, 2, and Supplement. 



Gomphoceras eximium, Hall. Fourteenth Rep. N. V. State Cab. Nat. Hist., p. 109. 18tfl. 



" "I " Illustrations of Devonian Fossils : Cephalopoda, pi. 44, fig-s. 1, 2. 1876. 



Shell large, straight, very gibbous ; exogastric. Transverse section subcircular 

 or very broadly oval. Longitudinal section subelliptical, with the point of 

 greatest gibbosity at the last septum. Tube enlarging very rapidly from the 

 apex, with the sides straight or somewhat concave for some distance, and 

 becoming convex over the last six air-chambers and the chamber of habita- 

 tion. Apical angle about 50°. 



Chamber of habitation large, having a length nearly equal to the diameter 

 of the tube at the last septum. The dorsal, ventral and lateral faces slope 

 rapidly to the aperture. Crenulations indistinct, with some traces of fine 

 transverse striae. 



The tube is slightly expanded at the aperture, but the particular features 

 have not been observed. 



Air-chambers regular, increasing in frequency from the apex toward the 

 outer chamber, varying in depth from five to ten mm. in a length of about 100 

 mm. ; the last three or four somewhat shallower than the preceding. 

 Septa smooth, thin ; concavity equal to the depth of two air-chambers. 

 Sutures straight and horizontal. 



Siphuncle nummuloid, distant from the ventral side twice its diameter 

 between the septa, which is equal to fourteen mm. where the tube has a 

 diameter of 100 mm., and equal to twice the depth of the air-chamber, or 

 twice its diameter at the septa. The surface of the constricted portions of the 

 siphuncular tube, at the septa, is radiated and surrounded by a distinct ridge. 



Test and surface-markings unknown. 



The largest individual observed, consisting of a portion of the chamber of 

 habitation and thirteen air-chambers, has a length of 185 mm., with a diam- 

 eter at the point of greatest transverse section of 115 mm. The portion of 

 the grand chamber remaining has a length of seventy mm. A smaller 

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