given original descriptions of new species, whether the specific names 

 be Carpenter's or my own, the types are understood to be the speci- 

 mens described by me, in the collection of the Academy ; wherever 

 and whatever the original Carpenteriau specimens may be. A case 

 in point is Ischnochiton acrior, p. 60, and I. conspicuus, p. 63. It is 

 only by this expedient that confusion can be avoided in cases of real 

 or fancied wrong identification, on my part, of Carpenter's Ms. 

 species. 



Many new species not illustrated in the body of the work are 

 figured from the types in the Appendix. The Appendix should 

 always be consulted when a species is not found elsewhere, as forms 

 of unknown generic position have been included therein. 



The grateful task remains of acknowledging assistance from 

 scientific friends and institutions. Through the intervention of DR. 

 WM. H. DALL, Honorary Curator of the Department of Mollusks, 

 U. S. National Museum, the writer has received from S. P. LANG- 

 LEY, Secretary of the Smithsonian Institution, the drawings and 

 MS. prepared by the lamented PHILIP P. CARPENTER upon this 

 group, a work of priceless value, embodying the results of many 

 years study of the subject. Throughout the text of this volume will be 

 found extracts from this MS. ; such quotations in every case being 

 carefully credited. For the loan of a large number of type spec- 

 imens from the Smithsonian collections, the writer is indebted to the 

 continued kindness of DR. DALL. To J. F. WHITEAVES of the 

 Canada Geological Survey, PROF. WHITFIELD of the American 

 Museum of Natural History, New York City, PROFESSOR F. W. 

 HUTTON of Christchurch, New Zealand, and many other con- 

 chologists, the thanks of the author are due for specimens presented 

 or loaned. 



H. A. P. 



