NOTES RELATIVE TO GAMBUSIA 179 
Camilla, Ga., in the Gulf Drainage, (Fig. 10); Huntsville, 
Ala. (Fig. 11); Memphis, Tenn. (Fig.12); Greenwood, 
Miss., (Fig. 13) ; Jacksonville, Tex., (Fig. 14) ; San Marcos, 
Tex., (Figs. 15-18.) Material was obtained from various 
other localities in Maryland, Virginia, North Carolina, Illinois, 
Indiana, Missouri, Georgia, and Florida. The drawings are 
reproduced at the magnifications indicated in the legend. 
It will thus be seen that the localities from which material 
was studied lie in three general sections of the United States: 
The Atlantic Coastal Plain, the Central Mississippi Valley 
region, and the Southwest. 
Material collected at the Mexican Border shows itself on 
examination to be typical Gambusia senilis,' a Mexican form 
which shows in the type of its gonopod-structure very 
striking and extensive dissimilarity to the material from the 
rest of the United States. (Figs. 15-18.) On comparison of 
the figures mentioned with those of gonopods of fish from 
other localities, it will be seen that the Mexican Border form 
is completely different. 
The material from the three general localities (with the 
exception just noted) also show differences, but not so 
striking, in the finer structure of the gonopod; differences 
that appear to be relatively constant. A comparison of 
Figures 1-5, 10 (Eastern form,) with Figures 6-7, 11-13 
(Central form,) and Figures 8-9, 14 (Western form,) il- - 
lustrates the differences. These differences are presented in 
tabular form in Table I: - 
This table shows that the structure of the third ray in the 
Eastern material is sharply dfferent from that of both the 
Central and Southwest material, for in the former there is 
a prominent series of posterior teeth on the proximal ossicles 
—a characteristic that is lacking in both the Central and the 
Southwest forms. The prominent longitudinal lateral ridges 
present on the third rays of the. Eastern form appear also 
to be entirely lacking in the Central and Southwestern forms.* 
* Since the above was written, material has been obtained from the 
“Central” region which shows lateral ridges; but these ridges do not 
appear to be nearly so prominent as in the “Eastern form.” 
