1884.] 



ISl 



ACANTEACLISIS OCCITANICA and A. B^TICA; A DIFFERENTIAL 



ESSAY. 



BY ROBERT McLACHLAN, F.R.S., &c. 



The comparative ease with whicli closely-allied species may be 

 distinguished is not always in direct proportion to the size of the 

 animals. This axiom is strikingly exemplified in the large Ant-Lions 

 for which Eambur (in 1842) pi'oposed the generic term Acanthaclisis* 

 Down to 1842 only one European species (occitanica, Villers, with 

 synonyms) had been described. Rambur added a second European 

 species (hcsfica). It was very recently that I found myself able, from 

 the materials in my collection, to differentiate two European species, 

 which could not be other than occitanica and Icetica, but concerning 

 which Eambur's descriptions left me uncertain, especially on one very 

 important point (alluded to in the remarks that follow). The diffi- 

 culty was increased because I possessed only the $ of one of the 

 species. I therefore applied to my ever-obliging friend, Baron de 

 Selys-Longchamps, who at once forwarded, for examination, the ^ type 

 of A. Jxstica, Hambur, in his possession. This cleared up the doubts 

 occasioned by an unlucky expression used by Hambur, and has enabled 

 me to put together the following notes, the result of former vain and 

 now successful attempts, on my part, to come to any definitive con- 

 clusion as to the distinctive characters of the two species. 



A. OCCITANICA. 

 General form more robust and average 

 size greater. 



Last joint of labial palpi shorter, more 

 suddenly clavate, with the apex rather 

 suddenly slenderer. 



Median longitudinal band on the pro- 

 notum furcate anteriorly (complete pos- 

 teriorly) . 



Anterior wings having a short hlacMsh 

 hasal line between the two cubit i ; the 

 two rows of pentagonal cellules in the 

 costal area strikingly unequal in size, the 

 upper heing much shalloioer than the 

 lower. 



A. B^TICA. 

 General form more slender and average 

 size smaller. 



Last joint of labial palpi longer, more 

 gradually clavate, the club more slender, 

 and not suddenly nai-rowed at its apex. 



Median longitudinal band on the pro- 

 notum separated into two lines for its 

 whole length by a central (sometimes 

 interrupted) line of the ground colour. 



Anterior wings with no blackish basal 

 line ; the two rows of pentagonal cellules 

 in the costal area nearly equal in size. 



* Since Rambur's time, discordant species, probably forming several generic groups, have been 

 located in Acanthadisis, many of which contradict the chaiacter upon which the generic term 

 was based 



