TACHINIDAE OF ORIENTAL REGION 47 



of greater taxonomic significance in the prosenines than in many other tachinid 

 groups, and I attach considerable weight to it in denning Dexia and determining 

 its synonyms. If all the Oriental genera so far described that possess the second 

 costal sector hairing are aggregated (i.e. all the genera described by Townsend 

 and above-mentioned) it is found that they give the impression of being a 'natural' 

 genus, and that they are then not distinguishable from European Dexia; thus I 

 use the common possession of hairing on the venter of the second costal sector as 

 one of the prime reasons for synonymizing the Townsend genera with Dexia. It 

 is particularly striking how the haired sector immediately differentiates Dexia 

 from other well known genera of its tribe such as Billaea, Diner a and Myostoma 

 in which the second costal sector is bare. 



The second complex to be found in the Oriental Prosenini in which I have taken 

 the broad generic viewpoint is that of Billaea Robineau-Desvoidy. Many so-called 

 genera have been described in various zoogeographical regions that are allied to 

 Billaea but that differ merely in the degree of development of the facial carina. 

 Most of these genera are untenable, for intermediates exist, and undoubtedly in 

 this complex the facial carina does not provide a valid generic character. I there- 

 fore agree very closely with Mesnil (19506 : 113) and treat Billaea as a genus including 

 forms both with and without a facial carina, and in conformity with him I consider 

 (for example) that the New World Paratheresia Townsend and Bathytheresia 

 Townsend (which lack the facial carina) are synonymous with Billaea. Likewise, 

 I here synonymize the Oriental genera Theresiopsis Townsend and Philotrichostylum 

 Townsend, both of which lack the facial carina but fall within the broad concept 

 of Billaea. The main characters possessed by Billaea, as the genus is here recognized, 

 are as follows. 



Billaea Robineau-Desvoidy. Head with or without a facial carina. Palpi well developed. 

 Proboscis short. Propleuron haired. Humeral callus with three or more differentiated 

 setae. Pteropleural seta differentiated. Nearly always two stpl setae. Four post dc 

 setae. Mid tibia usually with two or three ad setae. Cell i? 5 open. Bend of vein M angulate, 

 usually with short M 2 appendix, near to wing margin. Second costal sector bare ventrally. 

 Abdominal tergites without discal setae and both sexes always without median marginal 

 setae on Ti -+- 2. Forms with robust build and short legs, often with the facies of large 

 Sturmiini. 



The faunal composition of the Prosenini in the Oriento-Australasian regions 

 shows some interesting features that deserve comment. The most conspicuous 

 feature of-the fauna is its impoverishment in New Guinea, where (on present evidence) 

 the tribe is represented only by the genus Prosena. The distribution of Dexia, 

 the predominant genus in the Oriental Region, appears to extend eastwards as 

 far as Celebes and there to stop so that no Dexia-like forms occur in New Guinea 

 itself or in the Pacific islands eastwards of New Guinea. Similarly, the genus 

 Senostoma, the predominant element in the Australian fauna, reaches into northern 

 Queensland but seems not to have entered New Guinea. Insufficient is known 

 of the hosts or potential hosts (presumably all in the Coleoptera) to determine 

 whether the striking difference between the Papuan fauna and that of adjacent 

 areas is associated with similar differences in the distribution of hosts. 



