Mr. Westwood's Observations on the Genus Derbe. 



Obs. Insertio venarum in medio alarum anticarum pauUo irregularis. In al^ dextra cel- 

 lula angusta basalis ad apicem emittit venam post venam bifidam (ut in fig. 2 Af), et 

 venae duae proximae sunt longitudinales (o et *) et disjunctae. In ala sinistra (fig. 2 B) 

 cellula basalis angusta versus apicem venam bifidam tantiim emittit ; vena proxima lon- 

 gitudinalis (fig. Bf) cum vena parva transversa venae postcostalis conjuncta est ; venaeque 

 proximas duae longitudinales sunt (fig. B, o et *), attamen ante originem conjunctae. 



Under the name of Mysidia I propose to arrange such of the South Ame- 

 rican species of these insects as have hitherto been described under the generic 

 name oi Derbe, but which differ from the typical species of the genus in various 

 respects, as indicated in the following contrasted characters of the two groups, 

 although they agree together in being exclusively inhabitants of South America. 



Mysidia. 



Statura debilis. 



Pedes breviores. 



Rostrum ultra pedes posticos baud exten- 

 sum. 



Antenna longitudine mediocri. 



Oculi rotundati. 



Ala breviores, latiores, tenerae, pulverosae; 

 anticte integrae ad apicem rotundatae; 

 vena mediastina (fig. 3 A, a) bifida, ramo 

 ejus antico ramulos nonnuUos obliquos 

 versus apicem emittenti, ramo postico 

 ad apicem bifido ; vena postcostalis (fig. 

 3 A, b) ad apicem trifida, venasque duas 

 alias longitudinales pone medium bifi- 

 das in medio postice emittens ; vena me- 

 dians (fig. 3 A, c) ramos tres emittens, 

 ramo medio bifido. 



Ala postica vena postcostali bifida aut tri- 

 fida (Tab. I. fig. 3, 4, B, z). 



Derbe. 



Statura robustior. 



Pedes longi graciles. 



Rostrum ad medium abdominis extensum. 



Antenna breviotes. 



Oculi subrotundati baud emarginati. 



Ala longiores, angustiores, nitidae; antica 

 ad costam ante apicem incisae, mem- 

 brana pone incisionem ramis tribus venae 

 mediastinae curvatae percursa ; mem- 

 brana reliqua venis numerosis regulari- 

 bus longitudinalibus in medio venis 

 transversis conjunctis percursa; vena 

 mediastina (fig. 1 A, a) bifida, ramo an- 

 tico ad apicem 4-ramuloso, postico ad 

 apicem bifido ; vena postcostalis (fig. 

 1 A, b) pone medium bifida, ramo an- 

 tico bis bifido, postico bifido ; vena me- 

 diana (fig. 1 A, c) ramos 10 longitudi- 

 nales emittens, quorum tertius e basi bis 

 bifidus. 



Ala postica vena postcostali quadrifid^ (fig. 1, 



