GENUS COLOCERAS. 21. 



Family— Triboloceratid2E, Hyatt, 188o (emend. LSI):}, 1900). 



Whorls similar to those of Trigonoceratidae ; periphery may be concave or 

 convex ; annular lobe in all genera except Coloceras. 



Genus Triboloceras (Hyatt, 1883, emend. 1893). — Shell discoid. Cross-section 

 subhexagonal. Periphery with a broad, elevated, median zone in the adult. 

 Prominent ridges on the sides and periphery, which are often rendered subspinous 

 by the_ coarse transverse lines of growth. 



Carboniferous. 



50. Triboloceras formosum.* 



Germs Vestinautilus (Byckholt, 1852, emend. Hyatt, 1883, 1893). — Shell thick- 

 discoid. Cross-section subhexagonal. Apparently smooth and. rounded in the very 

 young stage of growth. Periphery broadly rounded, with more or less distinct 

 ridges both on the sides and periphery, tending to become obsolete in the adult or 

 senile stage. Thick nodes are sometimes present upon the latero-peripheral angles 

 of the body-chamber in adult shells. 



Carboniferous. 



51. Vestinautilus semiglaber .* 56. Vestinautilus crateriformis.* 



52. „ erassimarginatus.* 57. ,, paucicarinatus. 



53. ,, cariniferus. 58. ,. pinguis. 



54. „ „ var. inagnicaineratus.* 59. ,, semiplicatus.* 



55. „ „ var. triplicatus.* 60. ,, niultiearmatus. 



Genus Planetoceras {Hyatt, 1893). — Shell subglobose. Cross-section pentagonal 

 in the adult, thus differing from Triboloceras and Vestinautilus. Body-chamber 

 partly free from the rest of the shell; greatly depressed and laterally expanded. 



Carboniferous. 



61. Planetoceras globatum. 



Genus Coloceras {Hyatt, 189:5). — Shell thick-discoid, section subquadrangular. 

 Periphery with numerous ridges in the early stages of growth and two elevated 

 /.ones on each side of a median depression. 



Carboniferous. 



62. Coloceras Covanum. (i:». Coloceras bistriale. 



