GENUS CCELONAUTILUS. 213 



Genus Poteiuocekas (M'Coi/, 1844). — Shell fusiform, the curvature slit^'lit, very 

 slender in the apical portion, inflated in the middle, contracting towaril.s the 

 aperture, which is simple. Cross-section nearly circular in the young, elliptical in 

 the adult. Siphuncle subcentral to marginal, moniliform. Body-clianil)er pro- 

 portionately large, constricted near the aperture. Test smooth. 



Ordoviciau to Carboniferous. 



'35. Poterioceras t'usifomie. 3(3. Poterioceras latiseptatuiu.* 



37. Polerioceras veutricosum. 



i^'aiH////— Taixocekatid.e, Hijaif, 1883 (emend. 1893, 1900). 



Discoidal, whorls usually robust, trapezoidal in section at some stage of growtli, 

 or throughout life, tuberculated ; sutures without annular lobe ; siphuncle small 

 and cylindrical. 



Genn.-i Temndcheilus {M'Cuy, 1844). — Shell subdiscoidal, umljilicus generally 

 large and deep. Periphery broad and flattened. Whorls usiudly but little 

 embracing ; cross-section trapezoidal at all stages of growth. One row of nodes 

 on each side of the periphero-lateral margin. 



Carboniferous. 



38. Temuocheilus corouatus. 



Famihj — Tuigonocekatid.e, Hijatt, 1883 (emend. 1893, 1900). 



Whorls subtriangular at some stage of growth or throughout life, often witli 

 longitudinal ridges; body-chamber sometimes free near the aperture. Annular 

 lobe rarely present. Siphuncle small, submarginal. 



Geum TiUGoNocEKAs (M'Coy, 1844). — Shell rapidly tapering, the apical part 

 forming half a volution {jide M'Coy), the rest gently curving. Cross-section scuti- 

 form. Peripheral area distinctly concave ; anti-peripheral edge carinated. Si])lnnu;le 

 subcentral in the direction of the peripheral area. Obtuse longitudinal ridges t)ceur 

 at the peripheral angles. 



Carboniferous. 



39. Trigouoccras paraduxicuui. 



Gi'iMS CiELONAUTlLUS {FounI, 1891, einunil. IlijuJI, bS'.l-)). — Shell eonipivssed - 

 discoid, deeply umbilicated. Cross-section subtriaugidar. l'eri[)heral area very l)road. 



