NEW MUSCOID FLIES FROM THE ANDEAN MONTANYA H? 



Peru- Ecuadorian frontier northward lowers still further and encroaches 

 rapidly on the coast strip until it reaches the Pacific at the Gulf of Guaya- 

 quil. From here to Panama it hugs the west coast constamtly and from 

 Costa Rica to Chiapas intermittently, but practically leaves it from Te- 

 huantepec to San Francisco Bay, where a preponderance of cirid to sub- 

 arid conditions again intervenes along the Pacific front, corresponding in 

 the north to the 2,000-mile desert stretch from Tumbez to Valparaiso. 

 South of Valparaiso and north of San Francisco it hugs the coast quite 

 continuously. From central Chile to central Peru it is practically absent 

 from the western slopes. 



The region in question, which may be known as the Andes-Rocky 

 Mountain montanya, exhibits a marked element of endemic tropical low- 

 land types from northwestern Argentina in the south temperate zone to 

 Venezuela, Colombia, Panama, Central America, and central Mexico in 

 the torrid zone, and the Sierra Madre of northern Mexico and the coastal 

 valleys of northeastern Mexico and southern Texas in the north temper- 

 ate zone. Some of its endemic intertropical mountain stocks, as exem- 

 plified in the bulk of the family Hystriciidae, reach an abundant develop- 

 ment as far north as the Sierra Nevada of California and the Rocky 

 Mountains of Colorado, though in a far less Veuriety of forms. Others, 

 as exemplified in the Hystriciid-like groups of the Exoristid subfaunily 

 P^rrhosiinae, seem much more nearly confined to the Andean region, 

 being here signalized by a most marked development. In the past the 

 whole region has drawn from the south many of the stocks which origi- 

 nated in Antarctica and her former dependencies or connections, and 

 from the north many of those which originated in Eurasia and northern 

 America ; in the present it draws on the descendants of these antipodal 

 elements engrafted on the native stocks, as they exist to-day in the two 

 Americas. From Bolivia to Ecuador occur its broadest contrasts in ex- 

 tremes of conditions ranged practically side by side. The Peruvian 

 montanya is in the heart of all this — in the great central region of its 

 highest evolutional activity. 



The flies comprised in the fcimily Hystriciidae and the Exoristid sub- 

 fcimily Pyrrhosiinae exhibit some of the youngest and most plastic stocks 

 of the animal kingdom. The variety of forms which they display in the 

 Andean montanya is marvelous and astounding until one realizes the 

 richness of this region in conditions favorable to their evolution. They 

 range from the low Amazonian plains at the base of the Andes up the 



