CEPHALOPODA. 349 



but sudden constriction, distant from the aperture about one third the length 

 of the grand chamber. Crenulated zone forming a narrow, deep fossa at the 

 base of the outer chamber, marked by sharp furrows, which arc continued 

 more obscurely over the posterior half of the chamber, becoming more 

 crowded and extended on the flattened portions of the dorsal and ventral 

 sides. 



Aperture large, trilobate, with one lobe considerably smaller than the 

 other two ; length equal to five-sixths of the width. Small aperture consti- 

 tuting the lesser lobe, longitudinally semi-oval, having a length of one-third 

 the greater diameter of the large aperture. Large aperture elliptical, lateral 

 diameter twice the length of the ventro-dorsal diameter. 



Air-chambers regular, having a depth of three mm., with the last one 

 somewhat shallower. Septa smooth, with a concavity nearly equal to the 

 depth of two chambers. Sutures straight and horizontal. 



Siphuncle small, near the ventral side, having a diameter of one mm. at 

 the septa, where the tube measures fifteen mm. in a ventro-dorsal direction ; 

 not observed in the cavities of the air-chambers. 



The test has a thickness of .75 mm. Surface marked by lamellose lines of 

 growth and fine, rounded, longitudinal striae. 



The length of the chamber of habitation, in the largest fragment observed, 

 is twenty-two mm., with a lateral diameter at the base of twenty mm. 

 A small individual, nearly entire, has a length of thirty-two mm., of which 

 fourteen mm. pertain to the chamber of habitation. 



This species bears considerable resemblance to G. claoatvm of the Schoharie 

 grit, in the curvature of the tube, the position of the siphuncle, the characters 

 of the chamber of habitation, and the depth of the air-chambers, but is distin- 

 guished by its larger aperture, smaller size, and the position of the plane of 

 greatest transverse section. In the size of the shell this species is included in 

 a group of small forms, to which belong G. beta, G. absens and G. davatum. 

 Two of these are endogastric in curvature, and two exogastric. 



Formation and localities. In the Goniatite limestone of the Marcellus shale, 

 near Schoharie, and at Manlius, N. Y. 



