
THE 
AMERICAN NATURALIST 




Vor. XXXVI. December, 1902. No. 432. 






STUDIES OF GASTROPODA. 



AMADEUS W. GRABAU. 
MARINE gastropods appear to have reached their acme of 
development in the present geologic period. What the 
Jurassic and early Cretaceous time was to the cephalopods, 
the Tertiary and present periods are to the gastropods. 
This is indicated not only by the great number of species, 
but also by the fact that so many series have branched out 
into bizarre types, in which excessive development of spines 
and tubercles suggests that the limit of variation is approached.? 
Phylogerontic types are furtl e to be found in the majority 
of series, while some groups, such as Strombus, Cyprza, etc., are 
represented only by phylogerontic forms in the modern seas. 
SO EDITOS 

3*9 


! The author has for the past five years been engaged in the study of the 
Phylogeny of gastropods, particularly the Fuside and some related types. 
monograph on Fusus and some of its allies is ready for the press, while another, 
dealing especially with Fulgur and its allies, is in preparation. The present paper 
is intended as a contribution to the principles of study of the molluscan shell as 
applied to Gastropoda, principles first worked out for the Cephalopoda by the 
~ late Prof. Alpheus Hyatt and some of his contemporaries, and for the Pelecypoda 
_ by Prof. R. T. Jackson. 
. 2 See Beecher, Origin and Development of Spines, Amer. Journ. of Sci., Ser. 4, 
vol. vi (1898), pp. 329-359; also Studies in Evolution., pP 93 et seg. Scribner, Igol. 
O17 : 

