134 LEAF-MINING INSECTS 



ing type, being equipped with cell-shearing mandibles. In 

 subsequent instars they feed more or less extensively upon 

 the tissues, and spin silken threads across the loosened cuti- 

 cle, causing the surface to become more or less ridged or 

 tentiform. 



There are two rather well marked groups of species within 

 the genus: 



1. The Lithocolietis group proper. 



2. The Cameraria group. 



The adults of these two groups differ but slightly, and 

 only in color, so far as noted. The white streakings of the 

 wings in the former group are dark-margined internally 

 while in the latter they are dark-margined externally. The 

 pupae differ in that a cremaster is always developed at the 

 caudal extremity of the body in the former, while in the 

 pupae of the latter there is none. 



The larvae of the two groups differ rather remarkably. 

 They differ both in form and habit. In the group of Litho- 

 colietis proper, after the change from the flat, sap-feeding 

 beginning, they are cylindrical in the fourth and later in- 

 stars, with the head of the form of ordinary free-living cater- 

 pillars. In the Cameraria group the larvae after the third 

 and last sap-feeding instar, continue to be depressed and 

 distinctly flattened in form, though less flat than before, 

 and the long axis of the head capsule continues in the same 

 plane with that of the body, and has the mouthparts pro- 

 truding in front. They further differ from first group larvae 

 in having dark bars or maculae laid across most of the body 

 segments both above and below. On account of this differ- 

 ence of form, in the larval stages that are most commonly 

 seen, they often become designated as "cylindric group" 

 and "flat group' ' larvae. 



Larvae of the first or cylindric group during their fourth 

 and fifth instars pick out the parenchyma from the network 

 of veins on the arched side of the mine, removing all the 



