T?isects. 



8055 



foveolate markings are too abruptly defined. This is very evident in 

 his figures of Ptiliurn canaliculatum and some of its allies. In all these 

 the thorax exhibits a central channel with an equally clear line on 

 either side ; but in many of these species the lateral lines are so faintly 

 impressed as to be perceptible only in a favourable light and under a 

 high power; though the central channel can almost be seen with the 

 naked eye. There is also another feature in Gillmeister's figures which 

 requires notice ; I mean the scale-like appendages at the ends of the 

 elytra in some of his Ptinellse. This is merely an optical illusion, and 

 is caused by the hinder margin of the first segment of the abdomen 

 seen through the transparent elytra and cutting off the rounded end of 

 each, thereby giving it the appearance of a semicircular scale. The 

 truth of this may be readily ascertained by raising the elytra with a 

 fine point. 



Except this short digression on Gillmeister's figures, all that I have 

 hitherto said refers exclusively to the species which I suppose to be 

 P. Ratisbonensis, and I think is sufficient to prove that all those varieties 

 belong to one and the same species. It is, then, reasonable to suppose 

 that a similar relation will be found to exist between other winged and 

 apterous insects in this remarkable group ; and although some species 

 may be invariably apterous, yet these appear to form an exception to 

 the general rule of the genus. 



Two species, P. gracilis and P. angustula, both as well or better 

 known on the Continent than any of their congeners, offer a good 

 illustration of this theory. The black eyes and fully-developed wings 

 of P. gracilis are the only points on which it materially differs from P. 

 angustula, its apterous analogue ; both of them exhibit the same dis- 

 tinctive characters in the shape of the head and thorax, and in the 

 slender and pointed abdomen. Strong corroborative evidence on 

 the same point may also be obtained from a new and very distinct 

 species which we found near Bakewell, Derbyshire. Of this, which is 

 widely removed from any known species by the shape of the thorax 

 and abdomen, and especially by the length and slenderness of its legs, 

 five specimens were taken, agreeing exactly with each other in all the 

 characters I have mentioned, one specimen alone being furnished with 

 ample wings, while the rest appear destitute of those limbs. The 

 question of thoracic fovea? is also affected by this species, the thorax 

 in two specimens showing two considerable depressions, although in 

 the others its surface is smooth. On the whole I do not see how we 

 can arrive at any other conclusion than that the wings are merely a 

 sexual mark among the species of this genus, and that in future other 



