S66 PALAEONTOLOGY OF NEW YORK. 



in regular, longitudinal lines along the tube. The chamber of habitation is 

 usually marked by a double constriction near the middle, with an interme- 

 diate ridge. The ventral side of the cast shows a longitudinal, ilattened area, 

 extending the entire length of the tube, and having a width equal to the 

 depth of the air-chambers. On the internal mould of the dorsal side there 

 is a low longitudinal carina, which is, however, not a conspicuous feature. 

 The surface shows lamellose lines of growth, which are raised into transverse 

 ridges or expansions atithe summits of the annulations of the internal mould. 

 The striae make a broad, retral sinus over the ventral side. 



The internal mould is very characteristic on account of the ornamentation 

 of the tube and the features of the ventral and dorsal sides. Sutures but 

 slightly impressed. 



The greatest diameter of the aperture of one individual is thirty-five mm., 

 and the chamber of habitation, with eighteen attached air-chambers, has a 

 length of 140 mm., of which forty mm. pertain to the grand chamber. 



The curvature of the tube, the characters of the siphuncle and the ornamen- 

 tation distinguish this species from any allied form. 



In this connection it is worthy of remark that the Cyrtoceras and Gvro- 

 ceras of the Upper Helderberg are characterized by a similarity in the surface 

 ornamentation, which generally consists of prominent, transverse, foliate expan- 

 sions of the test. In the Goniatite limestone we meet with the species here 

 described and G. transversum, both of which have the tube ornamented with 

 nodes and transverse undulations. A similar variation is also exhibited in the 

 species of the genus Nautilus, which are generally without special surface orna- 

 mentation; but the forms occurring in the same formation included under the 

 genus Discites of McCoy, are intermediate in character to the Devonian and 

 Carboniferous types of Nautilus. 



These transitional characters of the fauna of the Marcellus shale are more 

 marked in its contained Cephalopoda, which, however, constitute the conspicuous 

 feature of the formation. 



Formation and locality. In the Goniatite limestone of the Marcellus shale, at 

 Schoharie, N. Y. 



