102 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



tions present on the elytra of the males, and according to the 

 colour of the adult beetles, but there are certain constant 

 similarities in details of structure. 



The size of these beetles never exceeds 3 mm. The breadth 

 is narrow in comparison with the length, and is uniform through- 

 out the body. The thoracic shield is in all cases of the same 

 width as the elytra ; the length of shield considered in proportion 

 to the total length of the beetles is similar. The colour varies 

 from yellow to dark pitch-brown ; variations of all grades of 

 colour may be seen in the beetles of one set of galleries. The 

 antennae and tarsi of the different forms are yellow. The tibiae 

 and femora are usually lighter in colour than the elytra. Hair is 

 present on all parts of the body. The thoracic shield shows two 

 distinct regions, a rough tuberculated front portion and a compara- 

 tively smooth hind region. The tubercles on the front region 

 are flat-triangular ; they point to the rear of the insect, and are 

 arranged in a concentric manner. Smaller tubercles and hairs 

 are to be seen between these larger triangular projections. The 

 surface of the rear portion of the thorax is sunk below the 

 surface of the rough front region. The heads of all the forms 

 of Pityogenes are almost entirely covered from above by the 

 thoracic shield ; the head is in all cases almost spherical ; the 

 front part of the upper surface ot the head carries numerous 

 elevations, which show a concentric arrangement similar to that 

 of the thoracic shield. The mouth-parts of all forms are very 

 similar to one another, and do not differ much from those of 

 other genera of the Family Ipidae. The rear portion of the 

 elytra of the males is excavated so that there is a more or less 

 circular impression; the characters by which the species have 

 been defined are chiefly those of the males. The remarks that 

 follow refer to males only. 



Characters of the Wing-Covers of P. bidentatus, Hbst., 

 and of its Varieties. 



In the males of this type and in the males of the varieties of 

 the type certain characters are common. The single wing-cover 

 is hairy over the general surface, which is covered with small 

 circular depressed areas ; these latter are arranged in lines 

 along the length of the wing-cover, and the depressions of any 

 one line are more or less opposite to those of the second row on 

 either side of it. They are found everywhere except on the 



