72 Repobt of the State Geologist. 



Our material is insufficient to justify a definite statement as to gain or loss of 

 umbilication or the stage at which, any such change may have taken place. 

 We content ourselves with the statement that the older shells present a 



45 47 



Figures 45-50. Manticoceras fasciculatum, Views of the protoconch and nepionic shell. x25. Fig. 45, pro- 

 toconch from its proximal side, showing scar of si ponal caecum ; fig. 46, rear view showing first and second 

 septum and mark of eiphonal caecum ; fig. 47, lateral showing protoconch, nepionic shell and first three 

 septa; fig. 48, rear view showing three septa ; fig. 49, fragment of nepionic and ananeanic shell, showing 

 distal end of protoconch : fig. 50, side view, showing ananeanic corrugations. 



relatively smaller umbilicus and hence indicate an increase of overlap of the 

 w horls toward or at maturity. 



Ornamentation. The opening of the neanic stage is marked by the 

 abrupt appearance of simple varices, but there appear to be very few of these 

 (not more than three or four) at equal intervals, as they begin to come in 

 directly in pairs. In this form they may be traced for a full volution before 

 there is any evidence of intercalary striae in the intervals. The grouping 

 of the varices in this duplicate way is not lost even after the introduction 

 of the finer accessory lines. Gradually the members of each pair become 

 more or less merged into each other and the result is an elevated ridge 

 grooved on top and separated from its neighbors by a tolerably deep 

 furrow. This is the condition through the third and fourth whorls, but in 

 later growth the striation becomes more diffuse. There is some similarity 

 here to the mode of introduction and development of the varices, and their 

 occurrence in Mdntio. eontracfatm, but we have elsewhere indicated the 

 actual differences and the distinction in ultimate effects. 



