OF TURBINATED AND DISCOID SHELLS. 



357 



The following measurements were then made, beginning from the second and third 

 whorls respectively : 



By the two first admeasurements the formula gives 



r = (1-645)^ = 1-1804. 

 By the mean of the ratios deduced from the two second admeasurements it gives 



r = (1-389)^ = 1-1806. 



It is scarcely possible to imagine a more accurate verification than is deduced from 

 these larger admeasurements, and we may with safety annex to the species Turhu 

 duplicatus the characteristic number 1*18. 



Buccinum suhulatum. 



A line was drawn from the apex of this shell across its whorls as in the last, and 

 the following admeasurements were similarly made. 



In verification of the above the following larger admeasurements were made, begin- 

 ning respectively from the last whorl, the last but one, and the last but two. 



