334 PAIJEOSTOLOQY OF NEW YORK. 



at the base of the chamber of habitation, but no traces of the furrows are 

 observed over the walls of the air-chambers. 



A fragment, preserving the chamber of habitation and five attached air- 

 chambers, has a length of 105 mm. The chamber of habitation shows a 

 length of sixty-five mm., with a lateral diameter at the base of nearly ninety 

 mm., and a ventro-dorsal diameter of seventy-three mm. 



Tbis species is distinguished by the characters of the chamber of habitation 

 and form of the dorsal and ventral sides, in which it differs from G. eximium, 

 G. mitra and G. impar. From G. gomphus it is distinguished by the point of 

 greatest transverse section, the curvature of the dorsal and ventral sides, its 

 smaller aperture, the absence of the low undulations of the tube, and its smooth 

 chamber walls in the cast. The specimen described is imperfect, but preserves 

 several of the minor specific features not observed in specimens from the 

 coarser limestones. 



Formation and locality. In the cherty beds of the Corniferous limestones, at 

 Lexington, Scott county, Ind. 



GOMPHOCERAS GOMPHUS, n. 8p. 

 PLATE — SUPPLEM EOT. 



Shell large, straight, exogastric. Transverse section oval ; lateral diameter 

 the longer. Plane of greatest transverse section through the chamber of hab- 

 itation, distant from the last septum one-third the length of the chamber. 

 Ventral and dorsal sides convex, with the curvature of the ventral side 

 somewhat greater than the dorsal. Tube gradually enlarging to the point 

 of greatest gibbosity, and contracting slightly toward the aperture. Apical 

 angle about 23°. 



Chamber of habitation large ; length equal to the greatest diameter of the 

 tube, or about one-third the apparent length of the entire shell ; slightly 

 expanded at the aperture. The sides are convex, and slope gradually 

 toward the aperture. The crenulated zone in the cast forms a broad, gentle 

 constriction at the base of the chamber of habitation, and consists of shallow, 



