Vlll INTRODUCTION. 



Owing to the kind assistance of friends a very large amount of 

 material has passed through 033- hands. Among others, I am 

 peculiarly indebted to my colleagues at . the Natural History 

 Museum, Mr. E. A. Smith, I.S.O., of the Zoological Department, 

 and Dr. Smith Woodward and Mr. Bulleii Newton of the Geological 

 Department ; to Dr. Kitchin of the Museum of Practical Geology ; 

 Dr. Scharff of the National Museum, Ireland ; Dr. S. F. Harmer, 

 then in charge of the collections at Cambridge ; Mr. James Reeve 

 of the Norwich Castle Museum ; and the Curator of the Concho- 

 logical Society of Great Britain ; who all freely allowed me to 

 work over the valuable collections in their charge. Whilst, when 

 early in the work it became necessary to visit Bath in order to see 

 Jenyns' types, Mr. F. Shum, the President, and Mr. E. C. Davey, 

 the Hon. Sec. of the Bath Royal Literary and Scientific Institution, 

 were most kind and assiduous in affording me every assistance in 

 my researches. 



Among private collectors, besides Mr. A. S. Kennard and 

 Dr. Johansen, thanks are more especially due and are hereby 

 tendered to : 



Dr. R. Bellini (for Italian specimens, including some from the 

 historic spring at Caserta), the late Dr. 0. Bottger, the late Rev. 

 R. Ashington Bullen, C. S. Carter, Major M. Connolly, J. E. Cooper, 

 Capt. W. J. Farrer, Dr. L. Germain of the Muse'um d'Histoire 

 Naturelle, Paris (for specimens from the Locard collection), J. W. 

 Jackson, Dr. F. F. Laidlaw, Dr. K. Lampert of the K. Naturalien- 

 sammlung in Stuttgart, W. A. Lindholm of Moscow (for specimens 

 from Russia and from Lake Baikal), Mrs. Longstaff, H. Lynge (for 

 Scandinavian specimens), A. Mayfield, J. N. Milne, 11 Marchese di 

 Monterosato, C. H. Moore, H. C. Napier, Dr. Nils Hj. Odhner (for 

 Scandinavian specimens), C. Oldham, H. Overtoil, 11. A. Phillips, 

 H. B. Preston, F. W. Reader (for kind and assiduous assistance in 

 the preparation of the photographs that form the basis of the plates), 

 Mons. A. Rutot of the Muse'e d'Histoire Naturelle, Brussels, 

 A. W. Stclfox, F. H. Sikes, E. R. Sykes, F. Taylor, Dr. J. H. 

 The'el of the Naturhistoriska Riksrauseum, Stockholm, J. R. Le B. 

 Tomlin, the late Major H. Trevelyan (who specially dredged some 



