C461 ) 



Plate XV. 



1. Rhiphiorhi/nchus rothsckildi Austen, 8 (type).* 



2. Pepsis elevata Fabr.* 



3. „ heros Fabr.* 



4. AIi/(/as praeffraiidis Ansteu, ? (type).* 



5. Acliias i-othschildi sp. nov., ? . 



'^* )J )J )J T) O • 



'• )) )> )) )) )) 



'^^ >I )) )> ») )> 



"^^ )) )i I) i> )> VvP^/" 



All figures are natural size. 



Note. — The type (<?) and the other three males and female of Achlas 

 rothschildi from Stephansort were collected by the late Herr Wahnes. 



The Rhaplilorhynchus and Mijdas were collected by Jose Steinbach in Bolivia. 

 The two Pepsis are figured because they are the " models " mimicked by the 

 Rlutphiorlii/nchi(« and the Mi/das respectively. A full knowledge of the life-history 

 of these two remarkable Diptera can alone determine whether this is a case of 

 " protective " or of " aggressive " mimicry. 



The four males of the Achias are figured to illustrate the very great difference 

 in the development of the eye-stalks. Walter Rothschild. 



• See Ernest E. Austen, " Two Kemarkable New Species o£ Diptera," Nov. Zool. Jlay 19011, vol. xvi. 

 pp. 129 131. 



