G 



THE NAUTILUS. 



whorls, 5.05. From Lewistown, altitude 4,792 feet, Large diam- 

 eter, 16.80; depth, 11.78; aperture, 7.66; number of whorls, 5.28. 



From the above it will be seen that the specimens at higher alti- 

 tude are diminished in size, as also in the number of whorls in the 

 shell, as is the case of those west of the main range. 



The following table of comparisons of ten average specimens will 

 give a better idea of the differences than can be given in any other 

 way : 



In examining the preceding table, it will be remembered that the 

 specimens from Lewistown and the Tobacco Root mountains were 

 taken east of the continental divide, all the others from the west 

 slope. The series ranges from 3,300 to 8,500 feet altitude. There 

 is a gradual diminution in each measurement, the smallest and hi<rh- 



O 



est specimens showing about one-third the dimensions of the lowest 

 and largest, with the whorls diminished almost two, or nearly one- 

 third. 



The two collections from the east side of the range show the same 

 reduction, but the series is much smaller. I thought there was an 

 rror in the altitude of those from the Tobacco Root range, but as 

 Mr. Douglass insists there is not, it appears that conditions there 

 must differ from those prevailing elsewhere in the State. 



WRITINGS OF JAMES G. COOPER, M. D., ON CONCHOLOGY AND PALAE- 

 ONTOLOGY, WITH LIST OF SPECIES DESCRIBED BY HIM. 



COMPILED BY WILLIAM ,T. RAYMOND. 



Abbreviations : Proceedings of the California Academy of Sciences, 

 first series: Pr. C. A. S. ; second series, Pr. C. A. S. (2). 



