PREFACE 



THE present volume comprises two papers : one on the Land 

 and Fresh Water Mollusks of Alaska, by Dr. Wm. H. Dall ; 

 the other on the Hydroids of the Expedition, by Prof. C. C. 

 Nutting. Dr. Dallas paper has not been previously published ; 

 Professor Nutting's appeared in the Proceedings of the Wash- 

 ington Academy of Sciences in May, 1901. The number of 

 new Mollusks here described is twelve ; of new Hydroids twenty. 



C. HART MERRIAM, 



Editor. 



WASHINGTON, D. C., 

 June 15, 1905. 



