Biology of the Membracidae of the Cayuga Lake Basin 313 



other types of development are built, and is apparently one of the most 

 generalized of the prothoracic processes. It may vary from a perfectly 

 simple short prong to a long, ornate projection often branched and 

 extravagantly decorated with barbs, spines, bulbs, and ridges (fig. 40). 

 So constant and so important is this posterior process that it has been made 

 the character on which the subfamily Centrotinae is separated. All 

 forms that have the posterior process wanting or so poorly developed 

 that the scutellum is distinct — and it would seem that the development 

 of the scutellum increases as that of the posterior process decreases — 

 have been placed in this subfamily, which as a result has received a 

 rather heterogeneous collection of genera (Fowler, 1894-97). 



In generic and specific diagnoses 

 the pronotal structures have been 

 more generally used than any other 

 characters shown in the family. 

 This is to be expected, from the fact 

 that they are prominent and quickly 

 noted. Moreover, they are on the 

 whole reliable and of much value. 

 In the use of such characters, various 



areas and processes have received p,^ 4^3 ^.^^^^,^ development of pos- 

 arbitrary names, which, while of terior process 



Httle anatomical significance, are of ^''^^^^'^ Bastm) 



assistance in making uniform the terminolog}^ used by systematic workers 

 in the family. A few of these are deserving of special mention. 



Metopidiuin (fig. 41, a) is a term originated by Fowler (1894-97: 1) and 

 commonly used by later authors (Van Duzee, 1908 a: 30) to designate that 

 area of the cephalic part of the pronotum reaching from the dorsum to 

 the base of the head. 



The humeral angles (fig. 41, b) are the swelhngs, very characteristic of 

 the family, found on the lateral margins of the prothorax usually just 

 above the bases of the forewings. 



The suprahumerals, or siiprahumeral horns (fig. 41, c), are the lateral 

 projections on the edge of the metopidium just above the humeral angles. 



The posterior process (fig. 41, d) is the posterior extension of the pro- 

 notum and is perhaps the most important and most commonly used 

 character of all the prothoracic structures. Its size, shape, and develop- 



