2 ANNALS NEW YORK ACADEMY OF SCIENCES 



I. Introduction 



The literature of the genus Cerithium is already extensive, including 

 papers which treat the subject from both the paleontological and the 

 zoological point of view. The genus is treated to a greater or less extent 

 in all general works on conchology, but such treatment is confined to 

 descriptions of the genus and of the different species referred to it, 

 without any attempt to trace phylogenetic relationships, and the same is 

 true, with few exceptions, of paleontological papers on the subject. 



Recently M. Cossmann [1906] has published a monograph on the 

 Cerithiidffi, in which he takes account of the relationship between differ- 

 ent forms and presents an elaborate classification of the various genera 

 and sub-genera included within the family. 



M. Cossmann's conclusions are largely based on characters appearing 

 late in the life history of the individual, and he lays especial stress upon 

 the various features of the aperture. The present paper, being founded 

 upon a different method of work, as explained below, necessarily reaches 

 conclusions somewhat different from those of M. Cossmann. 



A complete bibliography of the works consulted in the preparation of 

 this paper is given on pages 86 to 91. 



The principles of phylogenetic development discovered and formulated 

 by Hackel, Hyatt, Cope and others have been successfully applied in 

 studies of the phylogeny of several groups of greater or less extent, such 

 as Hyatt's studies on the Cephalopoda, Jackson's on the Echinodermata 

 and Grabau's on the Fusidse. The present paper is an attempt to apply 

 these principles in working out the relationships of such species of 

 Cerithium as could be obtained. 



The fundamental law upon which all the work is based is the law of 

 morphogenesis, which has been stated by Hyatt^ as follows: 



A natural classification may be made by means of a system of analysis in 

 which the individual is the unit of comparison, because its life in all its 

 phases, morphological and physiological, healthy or pathological, embryo, 

 larva, adolescent, adult and old (ontogeny), correlates with the morphological 

 and physiological history of the group to which it belongs (phylogeny). 



According to this principle, a study of the life history of individuals 

 furnishes a ready and most reliable means of tracing the development of 

 the group to which they belong. Hence, in the present investigation, 

 the starting point has been the study of individual development and a 

 comparison of the records thus obtained. Similarity in the character 



1 A. Hyatt : "Genesis of the Arietidfe," p. viil. 1889, 



