NOTES RELATIVE TO GAMBUSIA 183 
are figured by REGAN, br of Mollienisia and Neoheterandria 
figured by HENN) also show a close adherence to a specific 
type of structure at the same time that they conform to a gen- 
eric type. Just as it has been possible for REGAN in his syn- 
optic paper to diagnose for each genus the microscopic struc- 
ture of the gonopod, so also does it appear possible to give 
diagnoses of the gonopod of each species. It appears con- 
_ clusively to the writer as the result of an extensive examina- 
tion of gonopods that by means of the structure of the gonopod 
alone it is possible to determine correctly the species to which 
a given top-minnow belongs. 
It is easily seen from these studies that the so-called “spec- 
ies” Gambusia affinis, as at present understood, is not a single, 
unified species. The Atlantic Coastal Plain form would 
appear to be sharply distinct from the other two forms, and 
hence merits the status .of a distinct species. It appears 
that it should be known as Gambusia holbrooki Grd. In the 
case of the two other forms the case is not so clear. The 
Central material obtained from Illinois, Arkansas, and Louis- 
liana (as well as other states) shows certain fairly constant 
differences from the Southwest material, as has already been 
noted. Since the differences found in the gonopod-structure 
of fish from the two sections are not of so fundamental a 
sort as those noted as existing between the Central and East- 
ern material, I should merely class the two as varieties and 
not call them distinct species. And as Gambusia affinis, is 
described earlier than G. patruelis in Baird & Girard’s 1854 
paper, it appears that the former name has the priority. 
SUMMARY. 
(1.) The Gambusia of the United States are usually included in one 
species, Gambusia affinis. 
(2.) REGAN has held on general anatomical grounds that there are 
three species, G. affinis, G. patruelis, and G. holbrooki, within the terri- 
torial limits of the United States. 
(3.) The microscopic structure of the gonopod in Poeciliid fishes 
has been proved by the work of a number of investigators to be a 
completely satisfactory criterion of generic and specific relationships. 
(4.) Study of the finer structure of the gonopods of material 
