516 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
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BIT Weg 
Ficure 6.—Only “true” limpet among these rock-clinging gastropods is the patellid at 
bottom, left. The others, quite similar in form, are, clockwise, Crucibulum, belonging 
to another order (Caenogastropoda), Haliotis, belonging to the superfamily Pleuro- 
tomariacea of the Archeogastropoda, and Diodora, another fissurellid. 
organisms had not yet lost one of their “sides.” They concluded that 
these primitive forms, unlike most gastropods, had possessed bilat- 
erally symmetrical soft parts (fig. 10). 
If this conclusion was true, then the paleontologists had discovered 
the probable ancestral group from which Jater gastropods were de- 
rived. Indeed, it seemed possible that not only were these forms 
(which are called monoplacophorans) the basal stock for the gastro- 
pods, but for the eight-plated chitons as well. Here, then, was some 
evidence with which to construct a new classification—one that had 
brought together two groups previously widely separated: the class 
Polyplacophora and the class Gastropoda. Such a classification is 
illustrated in figure 7. This new interpretation made it possible, for 
the first time, to relate two diverse groups as well as to understand 
something of the evolution of these groups. 
The never-ending labor of classification, whether it is the work of 
biologists or paleontologists or others, receives contributions from all. 
Shortly after the Smithsonian paleontologists’ announcement ? of this 
particular revised classification, a serologist—studying blood types 
in the mollusks—proved that the gastropods and chitons could not 
2 Knight, J. Brookes, Primitive fossil gastropods and their bearing on gastropod classifi- 
eation. Smithsonian Mise. Coll., vol. 117, No. 138, October 29, 1952. 
