98 



Report of the State Geologist. 



attained its minimum, the overlap of the fourth upon the third volution being 

 now the greatest. We may be justified in regarding this volution, as the 

 exemplification of the early ephebic stage and the period of establishment of 

 mature traits. It is not possible to delimit the perdurance of such features 

 without modification, but it may be observed that in a fully completed shell 

 there are two or three more volutions. These whorls show two very 

 excellent evidences of senility ; (1) the increase in umbilication ; (2) the 

 close crowding of the septa. They are also characterized by gradual filling 

 up of the depressed ventral groove and its loss of definition. 



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