5. DYSMACHUS 659 



" division can be attained if these middle forms be brought into the genus 

 " Entohnus, with the exception of those whose near aflfinity to species of 

 " Dyi^mnchus is so unmistakable that their generic separation would be 

 " unnatural." This distinction is very unsatisfactory, and has led Hendel 

 (Wien. Ent. Zeit., xviii., Ill) to the reactionary opinion that nearly all 

 Loew's genera formed out of Asilus are untenable ; I cannot however 

 agree with this opinion, though I admit that there exist occasional species 

 which may be difficult to locate with absolute certainty. 



Taking the three genera, Dysmachm, Entohnus, and Marhimus, it 

 cannot ad'i to the ease of naming a specimen if all be included in 

 one genus, because the difficulties will still have to be surmounted. On 

 the other hand when both sexes of a species are known a very large 

 number can be at once allocated and only a very few left in doubt 

 between two genera (one genus being always eliminated and one-third 

 of the difficulty overcome) ; for instance a female Machimus can at once 

 be distinguished from the other two genera by its free anal lamellae, while 

 a male Machimus cannot be confounded with Dysmachns because of the 

 produced eighth ventral segment; a female may be difficult to allocate 

 between Bysmaehus and Eutolmus, and a male with a produced eighth 

 ventral segment may be a Machimus or a Eutolvius, while one with a 

 simple eighth ventral segment may be a Eutolmus or a Dysmachus. In 

 most cases a Dysmachus may be distinguished in either sex from a 

 Eutolmus (apart from the anterior bristling or strong hairs of the thorax) 

 by its smaller size and by its black legs with at most only the base of 

 the tibiae reddish, and consequently a large species with a good deal of 

 reddish colour about the legs must be a Eutolmus. 



Dysmachus consists of about thirty Palaearctic species, of which the 

 great majority have been well distinguished, but only two are known 

 to extend to Northern Europe and at present only one has been found in 

 Britain. One or two species are said to occur in South America, but such 

 records must remain doubtful until the distribution of the genus has been 

 worked out by someone competent to recognise its characters. 



1. D. trigonus Meigen. Light grey with darker markings. Thorax 

 with long bristles on the middle line quite to the front part. Legs 

 slightly reddish at the knees. Genitalia short {6), sabre-shaped ( ? ). 



A very bristly species, with numerous very conspicuous 

 white bristles on the abdomen. 



$ , Face moderately wide and gradually widening downwards until it is nearly 

 twice as wide at the mouth as near the antennte ; above the antennae the 

 frons widens out very slightly but soon becomes slightly narrower again and 

 remains so up to the vertex ; face covered with whitish grey dust, which is 

 however less dense on the facial knob, and which may have a faint yellowish 

 tinge ; the upper third of the face (when measured from the uppermost 

 margin of the mouth) and also about the side thirds are bare, but the broad 

 sides of the mouth make the face appear to be longer and nearly the two- 

 thirds of those mouth-sides next to the eyes are bare ; facial knob rather large 

 and rounded but not very prominent ; face-beard covering the whole knob, long, 

 drooping, and abundant, mainly white or yellowish white or even pale orange 

 but with ])lack l)ristly hairs down its outer edges (though not at the topmost 

 part), and the bristly hairs on all (or more than the lower half of) the sides of 

 the mouth exclusively black ; the black hairs on the prominent part of the 



