GENUS COLOCERAS. 215 



Familii—Tnmn.urKUxnD.v., Hi/nll, 188:] (cmeiul. 1893, 190U). 



Whorls similar to those of Trigonocoratida? ; ])L'i'iph(.'ry may be concave or 

 convex ; annular lobe in all genera except < 'oloccni^. 



Genus Tuibui,(K'ki;as (Hyatt, 188o, emend. 189o). — Shell discoid. Cross-section 

 subhexagonal. PeriplKuy 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 formosuni.* 



Qenm Vestinautilus {Ri/rkholt, 1852, emend. Hijatt, 1883, 1893). — Shell thick- 

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

 young stage of growth. Periphery Ijroadly 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-periphcral angles 

 of the body-chamber in adult shells. 



Carboniferous. 



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



52. ,, crassimargiuatus.* 57. ,. paucicarinatus. 



53. „ cariuiferus. 58. ,. piuguis. 



54. ,, ,, var. maguicameratus.* 59. ,, semiplicatus.* 



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



Gcnm Plan!;tii(i;ka8 {Ili/dtt, 1893). — Shell sul)globose. Cross-section pentagonal 

 in the adult, thus differing from Trihuluceras and Vest iiuiiit tins. Body-cliamber 

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



Carboniferous. 



61. Plauetoceras globatum. 



Genus Coloceras {Hijatf, 1893). — Shell thick-discoid, section subquadrangular. 

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

 zones on each side of a median depression. 



Carl^oniferous. 



62. Coloc<jras Coyauuui. 68. Coloceras bistriale. 



