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, 
sharp, 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. 
