108 Proceedings of the Biological Society of Washington: 



Rana burnsi, sp. nov. 

 Measurements of the type specimen: 



Width of head at rear of ear drum 24 mm. 



The web of the hind foot is quite variable. In the type it appears as a 

 keel on the sides of about two and one half joints of the longest toe, but is 

 clearly visible practically to the end of that toe. In some other specimens 

 it is much larger and stretches almost directly across between the tips of 

 the toes. There is every degree of variation between the two conditions. 



The color is extremely variable in each individual according to conditions 

 of fear, etc., as well as in response to the color of the environment but is 

 very uniform in the species as a whole. 



The color of this species is usually some shade of green or brown, varying 

 from the color of an old watersoaked board to a very light mist gray and to 

 a light apple green. About a third of the specimens have irregular black 

 spots on arms or legs or both. These spots never approach the condition 

 of regular cross barring so often seen in Rana pipiens. They look more like 

 blots of ink that might have gotten there accidentally. 



The brown color changes of Rana burnsi match almost exactly the similar 

 changes of the Wood Frog, Ra7ia sylvatica, the main difference being that 

 the latter species seldom shows a strong green color and always has a black 

 patch at the side of the head, which is lacking in Rana burnsi. 



Rana burnsi has been known for some years and is generally considered 

 simply an immaculate form of Rana pipiens. Breeding experiments may 

 show that this view is correct. The author believes, however, that there 

 are sufficient grounds for giving it a separate specific name, in the present 

 state of our knowledge of the group. 



The species seems to be confined to northern Iowa and southern Minne- 

 sota, with possibly some stragglers in western Illinois and Wisconsin. It 

 seems to differ from Rana pipiens only in color but no intergrading forms 

 have yet been found in the examination of many thousand specimens. In 

 size it is a very little smaller than Rana pipiens. That is, the very largest 

 individuals of the latter species are a little larger than the very largest ones 

 of the former. In length of leg and in the webbing of the hind foot Rana 

 pipiens is extremely variable and Rana burnsi is within the range of varia- 

 tion. Some specimens of Rana pipiens have very short legs while others 

 have very long ones. In different individuals the heel reaches from eye 

 to end of snout. Some specimens have two whole joints of the longest 

 toe free from the web while others have almost as large a web as a Bullfrog. 



