5 '4 TRANSACTIONS OF THE WAGNER FREE 



divisions of the orders have been ranked as superfamilies, rather than sub- 

 orders, as formerly, as it seemed as if this term more fairly expressed their 

 relative rank. 



No attempt has been made to revise the nomenclature of these lists, except 

 in a few obvious cases ; in general they have been taken from the Manuals. 

 Subgenera have only been mentioned when there seemed to be special reason 

 for so doing, but the writer does not wish to be understood as expressing in 

 this place any fixed opinion as to the validity of the genera cited. When a 

 name, family or generic, is preceded by a mark of interrogation, it will be under- 

 stood that a doubt is intimated as to the proper location of the group in the 

 system ; when the mark of interrogation follows the name, there is question as 

 to its value or validity as a group. 



In a work of this sort, which necessarily depends largely on the literature 

 for its data, it is not practicable, for reasons of space, to refer every item to its 

 source. All accessible sources have been consulted and especial use has been 

 made, on the paleontological side, of the works of Neumayr, Zittel, Hall, Stol- 

 iczka, Steinmann, Bittner, Paul Fischer, Dr. R. T. Jackson and E. O. Ulrich ; 

 as regards morphology, Owen, Hancock, Deshayes, Paul Fischer, W. Clark, 

 Arthur Adams, Jeffreys, Coupin, Pelseneer, Menegaux, Rawitz, Grobben, J. 

 L. Kellogg and others have been laid under contribution. Whenever alcoholic 

 or fresh material has been accessible, it has been compared directly with the 

 literature, with useful results in many cases. Recent observations by the 

 writer on several deep-sea forms have thrown light on several vexed ques- 

 tions. 



In general the impression derived by the writer from this review of the 

 characters hitherto available for classification, is confirmatory of the opinion 

 previously expressed, that no classification based on single characters will be 

 permanent and that we may anticipate much from the continued, more thorough 

 and more rational study of the fossil forms taken in connection with their 

 recent analogues. Such work as that of Hyatt, Branco, Waagen and Jackson 

 is the best refutation of the short-sighted and narrow views which have been 

 expressed by sundry budding morphologists, as to the nature and systematic 

 usefulness of the shelly parts of the anatomy. There can be very little doubt 

 that a more thorough exploration of the deep sea will greatly enlarge our 

 knowledge of anatomic modifications in the Pelecypoda, since it would seem 

 that, in that region, not only may certain most interesting specializations 

 abound, but many archaic features, which have wholly disappeared in the com- 

 petitive struggles of the shoal- water fauna, are still retained in an approxima- 

 tion to their original form. 



The minute study of successive faunas in a single region, which is nowhere 

 more practicable than in the region of our Southern Tertiary, will, without 

 doubt, throw great light on the development of many groups, when studied in 

 connection with the dynamic relations of the parts of the organism. With 



