26 ANNALS NEW YORK ACADEMY OF SCIENCES 



is ornamented by two strong, equal spirals, with two finer spirals on the 

 shoulder and all the spirals crossed by ribs. The succeeding volution 

 has a fine spiral intercalated between each two of the three already exist- 

 ing, and more spirals are rapidly introduced on the later volutions. The 

 spirals on the adolescent and adult whorls of this shell are all flattened^ 

 their limits being defined only by the exceedingly fine grooves between 

 them. The lower primary spiral begins to decrease in strength on the- 

 sixth volution, and the seventh has a sharply angled outline. On this 

 volution a row of fine nodes is formed just below the upper and above- 

 the lower suture. On the body volution the shoulder is lost, and the 

 surface is ornamented by five or more rows of low nodes. 



The aperture is oval. The callus of the inner lip is thick and has a 

 strong posterior tooth. The outer lip is thick and smooth. The an- 

 terior canal is short and slightly bent backward. 



HoKizoN AND LOCALITY : Receut. Mediterranean Sea. 

 No. 20131, Columbia University collection. 



Eemarks : Centhium mediterraneum has its nearest relative in C. citri- 

 num mut. hicolor. It difi:ers in having flattened spirals not grouped 

 in bundles, as in the latter species. On the whorls having an angular- 

 outline the reduced primary spiral becomes so much flattened that the 

 outline of the lower as well as the upper slope of the volution is nearly 

 a straight line. In the preceding species, which are similar to C medi- 

 terraneum, the lower primary spiral is always stronger and easily distin- 

 guishable from the secondary ones. From C. columna this species differs 

 in having finer surface ornamentation, with flattened spirals and broader- 

 ribs and in the loss of the shoulder on the body volution. 



The last five species and one variety, namely, C. menhei, C. columna, 

 C. citrinum and its mutation hicolor, C. scabridum, C. mediterraneum, 

 constitute a group of closely related forms. They are evidently all de- 

 veloped from a common ancestor and for the early portion of their life 

 history follow the same path of development. The divergence observed 

 in the neanic and ephebic stages of growth are all due to difPerences in 

 the degree of development or in the grouping of the various features of 

 the surface ornament. In C. menl'ei the development of the spirals and 

 the sharply angled outline of the whorls are emphasized; in C. columna 

 the development of the shoulder and of the ribs are distinctive, and in 

 C. citrinum and its variety the grouping of the spirals in clusters is no- 

 ticeable. They might all be regarded as varieties of one species, as sug- 

 gested by Tryon, or their divergence in the adult stage might be con- 

 sidered great enough to entitle them to rank as distinct species. The- 



