386 



LOWER VERTEBRATES. 



exceptional in having a longitudinal row of teeth on the roof of the mouth, on the 

 parasphenoid bone. Most of the largest species of this series belong to the genus 

 Sypsiboas. This is characterized by the presence of a thumb, in which the last 

 phalanges are co-ossified into a curved spine of dense translucent bone, with a very- 

 sharp ajjex. This is concealed in a sheath of skin, but readily penetrates an object 

 against which it is pressed. This is another arrangement for enabling the male to 

 maintain his hold on the female during the season of breeding. 



In the genus Phyllomedusa, the middle toes of both feet are reduced in size exactly 

 as in some genera of African lemurs (Arctocebus, etc.), so that the external toes oppose 



Fig. 200. — Nototreuia marsupiatum. 



each other. This is an adaptation to the habit of seizing a limb round it, a mode of 

 securing a hold different from that which prevails in the family generally, where the 

 toes are attached to flat surfaces by adhesion of their terminal discs. Accordingly 

 the discs are small in Phyllomedusa. This genus is connected with the central 

 form Hyla by intermediate forms, especially by the genus Agalychnis. Of the 

 ninety-five species of the genus Hyla, the largest are the H. dolichopsis of Xew 

 Guinea, and the JT. vasta of the "West India island of San Domingo. The head 

 and body are five inches long in both. They are exceeded in dimensions by the 

 Phyllomedusa bicolor, which occasionally reaches seven inches. The smallest Hyla is 

 the H. piclceringii, which is an inch and less in length. The common Eyla of the 



