630 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 51. 



Among the important causes of the present confusion in the Lepa- 

 dellids, allowance must be made for the variability of some of the 

 species, notably of Lepadella patella (Miiller) and L. ovalis (Miiller) ; 

 intimately connected with this is the fact that material from a suffi- 

 ciently large territory to ascertain the limits of these variations has 

 not been at the command of any one investigator. The writer has 

 been very fortunate in having access to an abundance of collections, 

 without which this work would have been impossible. 



Through the kind intervention of Dr. Chancey Juday, of the Uni- 

 versity of Wisconsin, to whom I am specially indebted, as well as to 

 Dr. E. A. Birge, director of the Wisconsin Geological and Natural 

 History Survey, I have had the use of the following material from 

 the all but inexhaustible storehouse of the Survey: 



Collections by Doctor Birge during the Great Lakes Investigations 

 by the United States Fish Commission in 1899. 



Collections from Texas, Louisiana, Arkansas, and Missouri, by 

 Doctor Birge and Doctor Juday in 1903. 



Collections from the Finger Lakes in New York, by Doctor Birge 

 and Doctor Juday in 1910. 



Collections from Washington, Oregon, Idaho, and California by 

 Mr. W. Boormann, of the University of Wisconsin, in 1910. 



Collections from Mexico, Guatemala, Salvador, and Nicaragua by 

 Doctor Juday in 1910. 



Collections from various points in Alaska by Mr. G. Dallas Hanna 

 in 1905. 



Collections by Mr. J. M. Jessup in 1911 and 1912 along the boundary 

 line between Alaska and Canada from the Porcupine River to the 

 Arctic Ocean. 



For material from the localities given below I am greatly indebted 

 to the following investigators : 



For collections made during the Smithsonian Biological Survey 

 on the Isthmus of Panama, as well as from Wisconsin, Utah, Colorado, 

 Yellowstone Park, and a number of scattered points, to Dr. C. Dwight 

 Marsh, of Washington City. 



For collections in the Pikes Peak region, Colorado, in 1904, to Dr. 

 Homer L. Shantz, of Washington City. 



To Mr. Charles F. Rousselet, who, with his usual kindness, has filled 

 in the gaps with material not obtainable elsewhere. 



To Mr. James Murray, who, on his way to join the iU-fated Canadian 

 Arctic Expedition, brought me material from his South American 

 trip in 1911. 



For collections from Southern California and from the vicinity of 

 Atlantic City, New Jersey, to my friend Mr. Frank J. Myers, of Beth- 

 lehem, Pennsylvania. 



