58 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



prosternal plate projecting slightly beyond the line of the body 

 and ending in two short but sharp hooks which no doubt aid 

 the larva in its movements. Not the least striking larval char- 

 acter of this family is the unusual shape of the mandibles, 

 which depart from the general rule of all known coleopterous 

 larvae by curving outward. This character has held good in 

 all species examined by the writer. The muscles are attached 

 to the mandibles in such a manner that when they contract, 

 instead of bringing the edges together they throw them apart. 

 Instead of biting or pinching the wood the mandibles act as 

 miniature rasps or saws. This, as can be seen from the broad 

 galleries of Tharops and Melasis, would be more useful to the 

 larvae than the usually fashioned ones. This theory of the 

 movement of the mandibles was substantiated by the writer 

 by observing through a microscope a larva of Melasis pectini- 

 cornis at work in its gallery. During the transformation of the 

 larva to pupa the mandibles change their form and position and 

 the adult possesses mandibles similar in general shape to those 

 of other beetles. The adults of the borers in sound wood pos- 

 sess very powerful mandibles and in Ncmatodes they overlap. 



Species that infest decaying wood are represented by only 

 two genera, namely, Fornax and Microrrhagus. The form of 

 the gallery and condition of the wood in which the larvae of 

 these genera live are very similar, except that Fornax has a 

 relatively larger mine. It has been suggested that the larvae of 

 these two genera make no definite gallery but simply push 

 their way through the soft wood, which closes behind them 

 and leaves no trace of their passage. While it is usually impos- 

 sible to trace a gallery its entire length, yet when the wood is 

 not in too far advanced a state of decay they are clearly visible 

 and may be seen curving about in the wood, running in a longi- 

 tudinal direction, then turning in a transverse one. 



There is an abundance of evidence that the larvae not only 

 make galleries in decayed wood but that they also occasionally 

 mine in solid wood. As an example of this the writer found a 

 large dead willow thickly infested with Forna.v badius larvae, 

 several of which had bored through the soft sapwood to a 

 distance of 3 or 4 inches into the solid heartwood. The mines 

 of species of this group are relatively small and more open than 

 those of the opposite one. The difference in size may be 

 accounted for by the fact that the wood is softer and more 

 elastic than solid wood, giving it a tendency to close behind the 

 larva, thus reducing the diameter of the mine and the soft, 

 damp state of the wood causing the borings to pack and adhere 

 more readily to the sides of the gallery. 



