CEPHALOPODA. 321 



GOMPHOCERAS FAX, n. Sp. 

 PLATE-SUPPLEMENT. 



Shell slender, slightly arcuate ; curvature exogastric. Transverse section 

 broadly elliptical ; lateral diameter the longer. Point of greatest gibbosity 

 near the middle of the chamber of habitation. Tube regularly and gradually 

 enlargng from the apex to the point of greatest transverse section, and 

 rapidly contracting to the aperture. Apical angle, in compressed specimens, 

 about 18°. Apex acute. 



Chamber of habitation large, with a length equal to the greatest lateral 

 diameter. Crenulated zone narrow, marked by fine, transverse furrows, of 

 which traces are remaining over each of the chamber walls of the internal 

 mould. 



Aperture small, suboval, slightly extended on the ventral side forming the 

 small aperture. Large aperture, having its longer diameter equal to two- 

 thirds the lateral diameter of the chamber of habitation. 



Air-chambers regular, numerous, with a depth of from two to five mm. 

 Septa smooth, so far as observed. Sutures straight and horizontal. 



Siphuncle small, close to the ventral side, not observed in the cavities of 

 the air-chambers. 



Test not preserved. The internal mould preserves traces of strong lamel- 

 lo.se striae near the aperture. 



A compressed fragment, consisting of the chamber of habitation and about 

 eighteen attached air-chambers, has a length of eighty mm. A smaller 

 individual, preserving the chamber of habitation entire, and twelve air- 

 chambers, has a length of sixty-seven mm., of which twenty-three mm. 

 pertain to the chamber of habitation. 



This species resembles, and is associated with, G. Illcenus, but is distinguished 

 by its much smaller aperture, which also differs conspicuously in general outline. 

 The fragment referred to 0. Illanus indicates a considerably greater curvature 

 of the tube than is shown in this species. It is further removed from G. clava- 

 tum and G. beta by the relative position of the greatest transverse diameter, 

 41 



