THR LARVA OF DICRANURA BICUSPI3. 197 



The Larva of Dicranura bicuspis {with plate). 



By J. C. DOLLMAN. 



The plate of the two diaf^rams, representing the larva of Dicranura 

 bicuspis, has been prepared from drawings taken of a larva which was 

 beaten from birch in Tilgate Forest on September 13th, 1901, by a son 

 of mine, while we were working for Cymatoplmra flvctuosa. It was on 

 the lower part of a young birch tree, which was about ten feet high, 

 and probably was descending for pupation to the main stem, for it 

 spun its cocoon, in captivity, the following morning. The larva 

 seemed an active, strong creature, and fed no more after capture, but 

 roved restlessly about the box containing the samples of birch bark 

 which were submitted for its selection. It was occupied in this way 

 until the noon of the day after being taken, when it settled on a piece 

 of bark, containing a depression, and therein quickly spun itself up, 

 without any change whatever taking place in its coloration. 



As is seen at a glance, the larva bears a strong resemblance to 

 those of Dicranura furcula and D. bifida, but its appearance differs 

 from theirs in many of the following respects. The general character 

 of its form is longer, more cylindrical, and more worm-like. The 

 texture of its skin is smoother, being free from the reticulated, or 

 granular, surface shown in its relations. The segments are not so 

 heavily accentuated, and it bears no lateral brownish-red ocellated spots 

 or blotches. The head is smaller than the prothoracic segment, into 

 which it can be withdrawn at will, and is of a rich chestnut-brown in 

 colour, without any grey or purple tendency, the cheeks of the face being 

 of a deep black. On the prothoracic segment, which frames the head, 

 are two blunt points, one on each side, from which a bold triangular 

 blotch is drawn to the dorsal summit of the mesothoracic segment, 

 terminating at its posterior edge in a pointed projection. This triangle 

 is of the same rich chestnut colour as the head, and it is divided by a 

 white tapering dorsal line, running from the crown of the prothoracic 

 nearly to the elevated point on the mesothoracic segment. The meso- 

 thoracic is the largest in diameter of all the segments, and gives a 

 suggestion of tadpole-like proportions to the whole creature. On 

 the dorsal area is a beautifully designed, elongated, saddle-shaped 

 marking, which begins on the metathoracic segment in an 

 isolated spot at its posterior edge, and which widens on the 1st 

 abdominal segment ; and again widens on the 2nd. On the 3rd 

 it is wider still, with a dip towards the lateral area. On the 4th 

 abdominal segment the saddle is at its widest, and extends downwards 

 to the spiracular region, where it all but touches the spiracle placed 

 upon it. On the 5th, Gth, and 7th abdominal segments it gradually 

 tapers, to extend again on the 8th ; where it forms a diamond-shaped 

 lozenge ; sharply finishing at the anal segment with a small black 

 plate. This saddle-shaped marking is of a fine variegated chestnut 

 tint, without any grey tendency, and is lightest in colour at its widest 

 part, as it is darkest also at its narrowest. The edges of it are firmly 

 accentuated by a bold rich line of red-brown, and from the 2nd abdo- 

 minal segment, longitudinally across the widest part of the saddle, is 

 a distinct dorsal line of a purplish colour, extending to the darker 

 colour on the 8th. On each side of this dorsal lino, on abdominal 

 segments 2 and 3, is a light distinct spot, considerably lighter than 



July 26th, 1902. 



