THE PRIMITIVE PORES OF POLYODOX SPATHULA 
(WALBAUM) 
HEXRY F. XACHTRIEB 
Professor of Animal Biology and Head of the Department, The University of 
Minnesota 
TWELVE FlGrRES 
Polyodon spathula, popularly called Spoonbill and Paddlefish, 
is one of the most individualistic and interesting representatives 
of the living Ganoids. Among the striking external features are 
hundreds of groups of black spots on both the dorsal and ventral 
surface (excepting a narrow area along the mid-dorsal and mid- 
ventral line) of the bill. The spots of a group may be arranged 
in two to five, or more, clearly marked smaller, primary groups 
of two to ten individual dots. Xow and then a single spot is 
located quite apart from others. As a rule the spots are grouped 
in the area corresponding to or lying over the meshes of the bony 
network of the bill. They rarely lie immediately over a plate 
of bone. Figs. 1, 2, 3, 4 will give a better idea of the arrangement 
and distribution of these spots on the bill of Polyodon than can be 
gained from a description. Similar groups of spots are found on 
the outer surface of the operculum, about the eye and other re 
gions of the head. Their distribution on the operculum and side 
of the head is shown in fig. 5. A large group may contain as many 
as sixty dots, but as a rule a group contains less than half that 
number, particularly on the bill. The largest groups have been 
found on the operculum. There is, however, considerable in- 
significant variation among the individuals in both the size of 
the groups and their distribution on the operculum and other 
parts of the head. On the bill the size of the groups of spots and 
their distribution are more or less determined by the bony net- 
work of the bill. Figs. 1 and 2 show their distribution on a large 
