396 PA UE0NT0L0G7 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 

 marly continuous, numerous annulations of that species. 



Formation and locality. In the Schoharie grit, at Clarksville, Albany 

 county, N. Y. 



TROCHOCERAS EtJGENIUM. 



PI. ATI. I.VIII, FIGS. S, 4; LXIX, FIGS. 10, 11. 



Trvcliocenu eugenium, Hall. Fourteenth Rep N. Y. State Cab. Nat. Hist., p. 108. 18G1. 



" " •' Illustrations of Devonian Fossils: Cephalopoda, pi. B9, figs. 8, 9. 1876. 



" gp.t " Illustrations of Devonian Fossils : Cephalopoda, pi. 48, tigs. 3, 4. 1870. 



Shell 6ubdiscoidal, 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-chambers regular, increasing in depth from the apex to the grand 

 chatnber, 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. 



