378 /' -i TO LOGY OF NSW TORE. 



throe of them varies from thirty to forty mm. Sinus abrupt, angular, having 

 a depth of about four mm. on the outer volution, and very marked in the 

 raised expansions. 



Internal mould marked by regular, prominent annulations, corresponding 

 in frequency to the external ornaments, and showing the longitudinal ridges 

 and furrows of the crenulations. 



The diameter across the disc, in a large specimen, measures 125 mm., and 

 the tube has a diameter of thirty-three mm. at the aperture. 



This species is distinguished from G. laciniosum by its nearly circular trans- 

 verse section, and more elevated and less regularly plicated transverse expan- 

 sions of the test. The annulations of the internal mould are much more 

 prominent and distant than in G. trivolve, and the transverse section is different. 

 In G. vndulatum and G. paucinodum the shell is characterized by several closely 

 coiled volutions. The specimens referred to this species show slight, but unim- 

 portant variations in the transverse section of the tube and the number of volu- 

 tions. This latter variation is principally due to the tendency of the outer 

 volution to become straight. 



Formation and localities. In the Upper Helderberg limestone, at Schoharie 

 and Catskill, N. J. 



Gykoceras undulatum. 



PLATES I.III, FIG. l-«; LIV, FIG. 5. 



f'yrtorrrwi undulatum, Vam'xkm. Geolog. Suit, of N. Y. : Rap. Third Dist., pp. 130, 140, fig. 2. 1842. 

 (fyroceras undulatum (Vanux.), Hall. Descriptions of New Species of Fossils, etc., p. 38. 1861 . 



Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 66. 1863, 

 " " Illustrations of Devonian Fossils : Cephalopoda, plate 



figs. 1, 2. 1876. 



Shell discoid, closely coiled, making from two to three volutions, which are 

 not contiguous. Transverse section broad, subangular transversely ovate; 

 lateral diameter the longer. The tube is somewhat flattened on the ventrum, 

 and angular at the ventro-lateral sides and on the dorsum ; regularly and 

 gradually enlarging. Apical angle about 7°. 



