18 GENUS TRIOHIOSOMA. 



On the underside the femora are grooved, and bear 

 a blunt tooth on either side at the apex of the groove, 

 but the inner tooth is very slightly developed ; and this 

 is pretty much the case with both in many females. 

 At the apex of the COXSB beneath there is a saddle-like 

 depression, with a tooth at either end as in Cimbex. 

 The metatarsus has a curved depression on the under- 

 side covered with hair as in Cimbex, but there is no 

 distinct spine at the apex as in that genus. The cal- 

 caria have a membranous loJbe at the apex ; the claws 

 are simple. As with Gimbex, the males have the legs 

 very much more developed than the females. 



The scutellum is flatter and longer than in Gimbex, 

 and at the base it projects forwards a little, so that 

 the depression at its base has a slight curve. 



The larvas are green, and when young are covered 

 over with a white powder. In form they agree quite 

 with those of Cimbex. One species feeds on birch, 

 another on Sorbus aucuparia, one on willows, and 

 another on hawthorn. 



Trichiosoma agrees very closely with Gimbex, and 

 by many authors the two are not considered generically 

 distinct. I certainly think the genus is a natural one, 

 and is sufficiently distinguished from Cimbex by the 

 blotch being absent, by the larger size of the labrum 

 compared to the clypeus, by the femora bearing teeth, 

 and by the body being covered with long hair. 



The genus is not so widely distributed as Cimbex, 

 and it contains fewer species. Four European species 

 are known, and three from North America. Possibly 

 one or two of the latter may not be distinct from the 

 Old World forms. 



Considerable variation is shown by the species, and 

 as the specific distinctions between them at the best 

 are not great, they are not always easily separated, 

 unless they have been bred, the Iarva3 here, as in many 

 other cases, affording the best criterion of specific 

 distinctness. 



