CEPHALOPODA. 395 



The specimens have a diameter, measured across the disc, of from forty- 

 five to seventy mm. A satisfactory determination of the elevation of the 

 spire cannot be given from the compressed and fragmentary condition of the 

 specimens. 



This species is distinguished from T. Clio by its more rapidly enlarging 

 tube, larger umbilicus, and the linear, lateral, annular nodes, which are not 

 continuous over the dorsal and ventral sides. In T. Biton the tube is more 

 gradually enlarging, and the nodes are less extended, reaching the greatest 

 prominence on the concave dorso-lateral faces. 



Formation and localities. In the Schoharie grit, Schoharie and Albany 

 counties, N. Y. 



Trochoceras Biton, n. sp. 



PLATE CXI, FIG. 7. 



Shell discoid. Transverse section very broadly elliptical. Tube regularly and 

 gradually enlarging. 



Chamber of habitation large, rapidly expanding toward the aperture, occu- 

 pying about one-fourth of one volution, and curving regularly with the volu- 

 tions of the helix. 



Air-chambers having a depth of about three mm. near the grand chamber, 

 as measured on the lateral face of the tube. 



Test thin. Surface marked by fine striae of growth, crossed by regular, 

 6harp, revolving striae, of which there are four in the space of two mm. 

 Tube ornamented with low, rounded, transverse undulations, which are 

 raised into prominent, short, linear nodes on the concave dorso-lateral face. 

 There are three in the length of twenty mm. on the grand chamber. Sinus 

 not observed. 



The specimen described is an imperfect fragment, consisting of the cham- 

 ber of habitation, and two attached air-chambers ; having a length of sixty 

 mm., and preserving distinctive characters. 



