PHYLOGENY OF FUSUS AND ITS ALLIES/== 



BY AMADEUS W. GRABAU. 



INTRODUCTION. 



The phylog-eny of Gastropoda has received hut Httle attention from 

 students of MoHusca, who have either confined themselves to the study 

 of faunas, and to specific description, or have investigated problems in 

 connection with the ontogeny of individual members of one or more 

 phyletic series. Besides the classical memoir of Hyatt, on the Tertiary 

 species of Planorbis at Steinheim, only two other important works which 

 are devoted to a study of the serial development of phyletic groups 

 have come to my notice. These are Koken's "Entwickelung der 

 Gastropoden vom Cambrium bis zur Trias," and an elaborate paper 

 by the countess Maria von Linden, in which she traces the development 

 of several genera of recent gastropoda including Conns, Voluta and 

 S trombus. Both authors make use of the successive types of orna- 

 mentation of the shell, and Countess von Linden uses furthermore 

 the successive changes in the color pattern of the shell as a means of 

 establishing phyletic relationships. 



The shells of Gastropoda are particularly well adapted for phylo- 

 genetic study, since all the stages from protoconch to the last stage 

 in the development of the individual are not only retained (provided 

 the specimen is perfect), but all of them are usually visible, so that 

 the study of the spire furnishes us with the means of differentiating 

 the successive stages in the development of any individual, which may 

 then be correlated with the adult stages of more primitive types of the 

 same phyletic series. It is a noteworthy fact that the chief changes in 

 the gastropod shell are at the periphery and on the shoulder of the 

 whorl, or, in other words, in those portions which are nearly always 

 exposed even after the addition of new whorls. It is thus usually 

 unnecessary to break down the shell, so as to get at the earlier stages, 

 as must be done with close-coiled cephalopod shells, when young 

 material is not available. Thus a single perfect gastropod shell will 

 reveal in its superficial characters nearly the whole life history of the 

 series to which it belongs. 



In determining genetic boundaries, the most important shell feature 

 is the protoconch. The genus should represent a phyletic series, in 



* Presented originally to the Facultj^ of Arts and Sciences of Harvard Uni- 

 versity as a partial fultillmont of the requirements for the degree of Doctor of 



Sciences, in May, 1900. 



I 



