344 PALAEONTOLOGY OF NEW YORK. 



GOMPHOCERAS OVIFORME. 



PLATES XLT, K1GS. l-» ; XLVI, FIGS. 6, 7; XCIV, FIGS. 6, 7. 



Gom})/ii>cer<u (Aplocenu) oriformt;. Hall. Thirteenth Rep N. Y. State Cab. Nat. Hist, ]>. 105. 1860. 



" iiri/cmir. Hail. Illustration! of Devonian Fossils: Cephalopoda, pi. 45, tigs. 1, 2. I87tf. 



Cyrtocerasi gibbosum, " Illustrations of Devonian Fossils : Cephalopoda, pi. 47, figs. 8, 4. 1876. 



Shell small, ovoid, or subglobose, gibbous, straight, exogastric. Transverse 

 section very broadly oval to subcircular. Longitudinal section regularly 

 ovate, sometimes attenuate at the apex. Plane of greatest transverse section 

 at the last septum. Tube rapidly enlarging from the apex, with the sides 

 concave for a short distance, and becoming convex over the greater portion 

 of the tube. Apical angle about 60°. Apex, when present, attenuate, acute. 

 Some of the specimens sbow a subsequent truncation of the apex : the 

 transverse striae lose their character, and the test is pitted or roughened. 

 This offers an explanation of the adhering matrix around the apex of many 

 of the specimens. 



Chamber of habitation comparatively large, having a length of from neatly 

 one-half to one-third the entire length of the shell, or about two-thirds the 

 greatest transverse diameter. Dorsal side more convex than the ventral, 

 and rapidly sloping to the aperture. The crenulated band forms a very 

 narrow fossa around the base of the chamber of habitation ; and shows flat, 

 shallow furrows continued over the grand chamber, and obscurely over the 

 walls of the air-chambers. 



Aperture large, trilobate, width equal to three-fourths the greatest trans- 

 verse diameter of the tube, or one-fourth more than the length of the entire 

 aperture. Minor aperture small, semi-circular, with a diameter of one-fifth 

 the major diameter of the large aperture. Large aperture elliptical, and with 

 its longer diameter equal to twice the length of the shorter diameter. In 

 the small specimens the whole aperture is comparatively smaller, and marked 

 by a variable constriction of the tube near the margin on the chamber of 

 habitation. 



Air-chambers regular near the chamber of habitation, except the last, 



