54 THE CANADIAN ENTOMOLOGIST 



THE CYRTID GENERA THYLLIS AND MEGALYBUS. 



BY F. R. COLE, BUREAU OF ENTOMOLOGY, FOREST GROVE, ORE. 



The genus Thyllis was established by Dr. Erichson in a monograph of the 

 Cyrtidae published in 1840. Four species were described in this paper^ all 

 from Capeland, South Africa. In the year 1865 Dr. Philippi described six 

 species of Cyrtidae from Chile, for which he erected the genus Megalyhus. In 

 1868 Schiner gave notes on two Chilean species in his '^'Reise der Novara," 

 recognizing in these two forms two of the species described by Philippi a few 

 years before. In this paper Schiner placed Megalybus as a synonym of Thyllis. 

 In a note he stated that there was no doubt in his mind that the genera were the 

 same, at least no character was given that would justify separation. In the 

 two species before him he noted that the eyes met above and below the antennae 

 and he continues, '"'whether this is the case with all Megalybus species I cannot 

 say, were it so, those Megalyhus species in which the eyes do not come together 

 under the antennae would be in another genus, that would then differ from 

 Philopota in the wing venation, from Thyllis by the eyes not joining under the 

 antennae." 



In 1876 Westwood described four species from Chile, stating "the names here 

 employed for this genus and its four species were found attached to the specimens 

 in Mss. when purchased, and have been retained, although, I believe, they have 

 never been published." Evidently Westwood had not seen Philippi's above 

 mentioned paper, for all four species were synonyms of those described by 

 Philippi and had perhaps been named from his collection. Neither did West- 

 wood compare the genus Megalyhus with Thyllis, to which it is so nearly related. 

 In his generic description he states that the eyes are contiguous above and below 

 the antennae. 



It would appear then that Schiner was correct in his synonym, but unfortun- 

 ately all of the Chilean species of this group do not have the eyes touching be- 

 neath the insertion of the antennae. My attention was called to this point when 

 examining specimens of what I take to be Megalyhus gracilis Phil, in the U. S. 

 National Museum. There are three specimens collected in Chile by Mr. E. C. 

 Reed. All have the eyes distinctly separated below the antennae. Mr. J. R. 

 Malloch informs me that all of his Chilean species of the genus Megalyhus have 

 the eyes separated below the antennae. Verrall, in his "British Diptera," considers 

 Megalyhus as a distinct genus. It may be that one sex has the eyes contiguous 

 below the antennae and the other has not ; if so, it is something occurring nowhere 

 else in the family. It is my opinion that the genera should be considered as 

 distinct, although they are very closely allied, as can be seen from the figures. 

 The species of Thyllis which I have figured has two median dorsal ridges on the 

 mcsothorax, which are not present in the Chilean species of Megalyhus. 



There are five genera in the Cyrtidae belonging to the remarkable group 

 Philopotina% if we consider Megalyhus as a genus, the others being Thyllis, 

 Philopota, Terphis and Helle. They are distinguished from all other Diptera 

 by the remarkable development of the prothoracic humeral lobes, Avhich meet 

 in front of the thorax in these forms. Most of the species have a grotesque, 

 hump-backed appearance. 



Some of the literature on the two genera under discussion is rather in- 

 accessible and I give a translation of the descriptions below. 



March, 1919 



