68 



THE NAUTILUS. 



It seems to the writer that the slow return of the snails dur- 

 ing the year 1914 was due not only to the repeated rains of the 

 fall and winter of 1913-14, but also to the condition of the creek 

 bed at this time. Although the heavy rains of 1915 were more 

 severe, they were confined to one month, and the creek bed was 

 left in a very much cleaner condition than during the preceding 

 year. 



The conditions of life which obtain now in Waller Creek are 

 those of a new life region. This must of necessity be so in an 

 intermittent stream to a certain extent, but owing to the flood 

 conditions here they are doubly so. 



The chief facts of interest in regard to the habits of snails as 

 shown by these observations, are these: 1, The snails of both 

 species are to be found commonly in uncontaminated water 

 which is running at a fairly rapid rate, and the most common 

 orientation is with the heads pointing up stream; 2, The snail 

 population in any stream is subject to wide fluctations depend- 

 ing upon flood conditions; 3, Physa because of its shape is less 

 affected by floods than Planorbis; 4, The return of the snail 

 population to a given stream is determined not only by the 

 frequency and severity of the floods, but also by the condition 

 of the bottom of the stream after the subsidence of the high 

 water; 5, The snails thrive best where there is a constantly 

 renewed supply of clean water which contains little decaying 

 vegetation. 



Wabash College, Craivfordsville, Ind. 



WILLIAM BULLOCK CLARK. 



Dr. William Bullock Clark, professor of geology in the Johns 

 Hopkins University, eminent for his contributions to geology, 

 died suddenly from apoplexy on July 27, at his summer home 

 at North Haven, Maine. 



Wm. Bullock Clark was born at Brattleboro, Vermont, De- 

 cember 15, 1860. Since 1894 he was professor of geology in 

 Johns Hopkins Univesity. In 1896 Professor Clark organized 

 the Maryland Geological Society, and has been State Geologist 

 since that time. The admirable volumes on paleontology of 



