Til K NAL ril.LS. 



A MOLLUSCAN STAMPEDE. 



31 



BY T. VAX HYXING. 



Ill the suiHiner o( 1899, wliile coUfctini: slu-lls in tlie viriiiiiy ot 

 Des Moines, Iowa, I iinide an obstrvatioii wliicli lias seemed to me 

 to be of more than ordinary interest. Aloiiji the margin of a bayou, 

 adjarent to the Des Moines river, I discovered what was iiiiite ap- 

 parently an old, abandoned cray-fish hole lie^ide an old stump. Clear, 



cold s|Miiig water was bubbling up tiom within tiie hole. oveiHowing 

 and ninniiig down tlie slo[)e about ten feet to the bayou. All the 

 way u|) the little stream, from the bayou to the hole, Physn gi/rina 

 was very numerous and in all stages of development, trom very 

 minute young ones \\\) to well-develo])ed adults. All were bended up- 

 stream and moving slowly towards the hole. AiouikI the margin of 

 the hole, and down in it as far as I investigated, al)out tburteen 

 incdies, the surface or wall of the hole was covered with tliciii one 



