Biology of the Membra cidae of the Cayuga Lake Basin 337 



Plate XXXV, 20. The median lobe at the head of the tibia is smooth 

 and polished and more or less spherical. Occasionally it is strikingly 

 different in color from the remainder of the leg and stands ovit in sharp 

 contrast; in a few species these rounded heads are snow-white and glisten 

 like shining pearls, in others they are brilliant orange or red and very 

 conspicuous. The}^ are not, however, very constant even within a 

 species, and therefore are not suitable for taxonomic characters. 



The general structure of the joint, on the other hand, shows some 

 interesting variations which appear to be constant enough to warrant 

 more careful attention from the standpoint of systematic work. In a 

 large number of forms studied, the structure proved to be distinct enough 

 between species, and occasionally between genera, to be of real assistance 

 in this respect, and, altho this structure has never been used in published 

 diagnoses, it is believed to be of value. A few of the types of variations 

 are figured in Plate xxxv, 21-26, these being chosen at random from 

 common genera. It may at first thought seem extravagant to attempt 

 to find in leg joints characters for taxonomic use. It must be remembered, 

 however, that the Membracidae are primarily a jumping family, and 

 the legs are used to a far greater extent than the .wings. It would not 

 1)0 surprising, then, to find modifications in leg structure comparable 

 to changes in wing structure in other insects, and, while it is not to be 

 supposed that such modifications are of great phylogenetic importance, 

 they may still be of enough value to warrant their careful consideration. 

 Moreover they are well adapted for study, since the leg usually projects 

 outward and l)rings the knee joint into a position which facilitates 

 examination. 



The tibia has attracted more attention in the Membracidae than any 

 other segment of the leg. This is because in certain forms of the family 

 this segment is broadly foliaceous and very striking in appearance. On 

 the basis of this peculiarity the genus Membracis, the type genus of 

 the family, was early separated (Fabricius, 1775:675), and the character 

 has since stood as the distinguishing mark of the subfamily Membracinae 

 which has been built up around this genus. This character in itself, 

 however, is not sufficient to distinguish the subfamily, since a number of 

 genera of the subfamily C'entrotinae show the same flattened, leaf -like 

 tibiae. It is valid only when considered in connection with the covered 

 scutellum. 



