CEPHALOPODA. 337 



Siphuncle ventral, internal ; its characters have not been fully observed. 



Test strong, having a thickness of two mm. over the chamber of habitation 

 and larger part of the chambered portion. Surface marked by fine, irregular, 

 lamellose lines of growth, and fine, regular, longitudinal strige. The surface 

 of the nacreous layer, as shown by the exfoliation of the epidermal layer, is 

 preserved as imbricating, lamellose lines, with obscure longitudinal striae. 

 The ventral side is indicated by a broad, decided sinus in the surface-strite. 



The internal mould is characterized by the smooth chamber of habitation, 

 the crenulated zone and the longitudinal carina, with traces of the crenula- 

 tions extending over the walls of the air-chambers. 



An individual, nearly entire, has a length of 180 mm., of which sixty mm. 

 pertain to the chamber of habitation. It preserves about twenty-five air- 

 chambers, and has a diameter of sixty-eight mm. at the point of greatest 

 transverse section. Another larger individual, imperfect at the apex, and 

 of the same proportions, has a length of 190 mm. 



This species is distinguished by its long, fusiform shape, the position of the 

 point of greatest transverse section, and its large aperture. It is not so rapidly 

 expanding and gibbous as G. eximium, and is of smaller size. A specimen found 

 in the drift in Michigan, and probably coming from the calcareous beds of the 

 Hamilton group, in the northern part of the lower peninsula, cannot be distin- 

 guished from the species as occurring in the Goniatite limestone of the Marcel- 

 lus shale. It is associated in New York with G. solidum, but in that species the 

 chambered portion is conical and rapidly enlarging, and the point of greatest 

 gibbosity is on the chamber of habitation, from which the slope of the sides to 

 the aperture is sudden and rapid. In the Goniatite limestone the specimens 

 are associated with Guniatites Vanuxemi and Orthoceras Marcellense. 



Formation and localities. In the Goniatite limestone, at Manlius, Onondaga 

 county, N. Y.; and in the glacial drift, at Ann Arbor, Mich. 



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