THE NAUTILUS. 15 



In studying these mollusks it is necessary to remember t' at the 

 different species often have an almost identical series of color varia- 

 tions, so that if one is guided chiefly by color, there is a liability to 

 put together mutations belonging to different species. There is little 

 doubt that food greatly influences and directly changes both the color 

 and texture of the outer layers of the shell, while the form is directly 

 related to the situs of the individual. 



An interesting fact in the distribution of these animals is the evi- 

 dence they give in favor of the probability of the former existence 

 of an elevated ridge or range roughly parallel with the coast of Cali- 

 fornia and the peninsula, and of which the Santa Barbara Islands, 

 Guadelupe, and Socorro are the only supermarine indications at the 

 present day. It looks as if there was a second gulf or inlet between 

 this range and that of Lower California, so that the cool-temperate 

 species were able to extend as far south as Socorro on the western 

 coast of the western range, while the more tropical forms were able 

 to reach far to the North in the warmer waters of the inner area 

 between the outer range and the continent to the east of it, including 

 what is now the Gulf of California. 



POSTPLIOCENE SHELLS OF PROVIDENCE AND LUPUS, MISSOURI. 



BY F. A. SAMPSON. 



Several trips to these two places have given many specimens. 

 Providence, Boone County, is on the north side of the Missouri 

 river, a place now of only a few houses, but formerly, in the days of 

 steamboat travel on the river, a large town and important shipping 

 point. The grading for the Missouri, Kansas and Texas railroad 

 along the river cut into the bluffs, and uncovered the deposits con- 

 taining great numbers of postpliocene land shells. The deposit is 

 of later period than the Kansas loess, and is not the fine silt of the 

 loess, but is of clay intermixed with stones of various sizes. 



Lupus is almost opposite on the other side of this river, in Moni- 

 teau County, where the grading for the river route of the Missouri 

 Pacific railroad uncovered the b^ds with the fossil shells. A mile 

 above Lupus was the former town and steamboat landing of Mt. 

 Vernon, a town of which no trace now remains. On both sides of 

 the river the rocky bluffs are of Chouteau limestone, resting on beds 



