396 
PALAEONTOLOGY OF NEW YORK. 
This species differs from T. discoideum in the position and smaller size of the 
linear, annular nodes. The tube is also apparently less rapidly enlarging. It is 
easily distinguished from similar fragments of T. Clio by the absence of the 
nearly continuous, numerous annulations of that species. 
Formation and locality. In the Schoharie grit, at Clarksville, Albany 
county, N. Y. 
Trochocer'as eugenium. 
PLATE LVIII, FIGS. 3, 4; LXIX, FIGS. 10, II. 
Tvochoceras eugenium, Hall. Fourteenth Rep N. Y. State Cab. Nat. Hist., p. 108. 1861. 
“ “ “ Illustrations of Devonian Fossils: Cephalopoda, pi. 59, figs. 8, 9. 1876. 
“ sp.f “ Illustrations of Devonian Fossils: Cephalopoda, pi. 48, tigs. 3, 4. 1876. 
Shell subdiscoidal, dextral, involute, making about one volution and a half, 
departing but little from a symmetrical coil. The apical portion is contigu¬ 
ous to the basal half of the grand chamber and several air-chambers. Trans¬ 
verse section subcircular, obtusely angular on the concave dorso-lateral mar¬ 
gin. The tube rapidly enlarges to a point near the middle of the chamber 
of habitation, and contracts more rapidly to the aperture. The diameter of 
the tube is doubled for about every half volution. 
Chamber of habitation large, gibbous, having a length equal to twice the 
greatest diameter, curved, and extending about half its length beyond the 
point of contiguity with the inner, adjacent volution. A narrow zone of 
crenulations, consisting of short, distinct furrows, crossed by one or more 
concentric lines, is continued around the base of the grand chamber, but does 
not appear on the internal mould of the air-chambers. Aperture contracted, 
opening direct, or at right angles to the spiral axis of the tube. 
Air-chanibers regular, increasing in depth from the apex to the grand 
chamber, varying from five to eight mm., measured on the lateral face of the 
outer volution. The last one or two chambers, usually somewhat shallower 
than the preceding. Septa smooth, having a concavity equal to the depth 
of the air-chambers. Sutures slightly curved and oblique, making a slight 
retral sinus on the ventral side. 
