PREFACE. 



THE classification of the " Pulraonata " will be essentially that 

 exhibited in the third volume of my " Structural and Systematic 

 Conchology ;" modified, nevertheless, as to minor details, and 

 chiefly by the introduction of additional groups. In the arrange- 

 ment and synonymy of the species, the late Dr. Louis Pfeiifer's 

 ' k Nomenclator Heliceorum Viventium," 1878, will be my princi- 

 pal guide, and I will endeavor so to intercalate the more recently 

 described species as to preserve the essential features of that 

 monumental work. Exceptions have been taken to Dr. Pfeiffer's 

 classification, as well as to his synonymy ; but I think that the 

 former will usually be found quite as progressive as the incom- 

 pleteness of material at present accessible will warrant ; whilst 

 the latter, which is more especially in the line of the late learned 

 doctor's life-study, ought certainly to be well digested, and worthy 

 of confidence. I shall not follow him blindly, however. I shall 

 consider the opinions of the special students of each local fauna 

 as entitled to great weight, and I shall constantly subject ques- 

 tions of synonymy to the test of comparison of specimens in the 

 admirable collection of terrestrial shells in the Museum of the 

 Academy of Natural Sciences of Philadelphia. 



The illustrations will usually be carefully-made copies of the 

 typical figures, accompanied, when necessary, by others showing 

 variations of form, sculpture and coloring. The Philadelphia 

 Collection includes authentic types and authors' examples of 

 numerous species heretoforeunfigured: these I shall have the pleas- 

 ure of including in my plates. Messrs. Edwin L. Sheppard and 

 John Ross, whose faithful and finished drawings of the marine 

 shells of the "Manual" have been much commended, will supply 

 the illustrations for this series also ; and the coloring will continue 

 in the hands of the experienced lady-artists who have worked so 

 faithfully upon the u Manual " since its beginning. 



In the arrangement of the text I shall continue the style of 

 the marine series. The figures will be relied upon to convey to 

 the student the more obvious specific characters, and only those 

 features which are obscure, or not likely to obtain immediate 

 recognition by the eye, will be dwelt upon. The differential 

 characters of nearly allied and easily confounded species will be 

 carefully stated. The coloration will always be described, for 

 the information of those who subscribe for copies of the work 

 with uncolored illustrations. 



GEORGE W. TRYON, JR. 

 ACADEMY OF NATUKAL SCIENCES, 



Philadelphia, January 1, 1885. 



