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THE AMERICAN NATURALIST [Vol. XLI 



relationships. Indeed the common practice of classifying largely 

 or wholly by adult characters has almost of necessity led to a mini- 

 mizing of the value of protoconchial characters when they are recog- 

 nized at all. When differences of protoconch features were found 

 in types classed together as related from adult characters it was 

 explained as the result of the influence of different physical condi- 

 tions acting upon the embryo. This heterostylism as it has been 

 called by Boettger/ is explained by him as probably having one of 

 two causes — either it is developed through a process of selection, 

 to give the animal a lighter shell, to enable the animal occupying 

 it to change its location more easily and quickly — or it has the 

 object to prevent the creature from sinking into the soft ooze of the 

 deep sea bottom, in which for lack of food or for other reasons it 

 would perish. This of course refers only to the young shell, for the 

 size of the initial protoconch whorl can have little significance in 

 the adult. 



Heterostylism, or a difference in the character of the protoconch 

 in individuals living under different conditions, has been shown 

 to exist in Murex irihulus L., where Sturany found that the deep 

 sea form differs from the littoral form in an embryonic end or 

 protoconch with more strongly swollen apical whorl, and with an 

 extra volution. Fusiis bifrons and F. paucicostatus are also dis- 

 tinguished at an early age by the relatively more swollen proto- 

 conch of the latter, which is at home in deeper water (490-876 

 meters) .2 



These two cases were used by Boettger ^ to illustrate his hetero- 

 stylism and to establish the non-validity of my contention that the 

 character of the protoconch of Fusus, of Clavilithes, Rhopalithes, 

 etc., are not only distinctive, but due to diversity of descent.* 



' Boettger, O. Ueber Heterostylie bei Schneckenschalen und ihre Erklaruiig. 

 Nachrichtsblatt der deutschen Malakozoologischen Gesellschaft; 1905, Heft 1. 



^ Sturany. Expeditionen S. M. Schiff Pola in das Rote Meer. Zoologif<che 

 Ergebnisse, XXIII. Gastropoden des Roten Meeres. Denkschr. Math. Nat. 

 CI. K. Akad. d. Wiss. Wien., 1903, Bd. 74. 



» loc. cit. 



*Grabau, A. W. Phylogeny of Fusus and its Allies. SmUhsonian Mis- 

 cellaneous Collections. Vol. XLIV, no. 1417, 1904. 



