432 INSECTA MADERENSIA. 



meet with any explanation of it altogether satisfactory) I have taken some paiiis 

 to investigate. The solution given by Mr. West wood, in his admirable Introduction 

 to the Modern Classification of Insects (vol. i. p. 356), would seem to come nearest 

 to the truth, but still it does not quite apply to the species imder consideration,— 

 ■which arc moulded, thus far, on one and the same principle. Mr. Westwood states 

 that the sound is generated by the friction of a polished portion of the scutellum 

 against the edge of tlu> prothoracic cavity. In Dei(calion, Farmena and Dorca- 

 dion, however, there is a narrow space, in the shape of an isosceles triangle (the apex 

 being turned towards the scutellum), which occupies nearly the entire length of the 

 nicsonotum, and which, from its brightness, appears at first sight to be perfectly 

 smooth. Allien viewed however beneath the microscope, this longitudinal area is 

 seen to be composed of very fine, transverse, parallel and acute ridges, closely set 

 together after the manner of a file : and it is by depressing and raising the pro- 

 thorax (an act which alternately exposes and re-covers the upper region of the 

 extremely cylindrical mesothorax) that its under side is brought to play against 

 this inner dorsal file, —by which process the stridulation is effected. In order to 

 con\incc myself of the reaUty of this, I have relaxed many specmiens of the genera 

 in question, and have caused the soimd artificially with the greatest ease. 



Hence, we can mimediatcly appreciate the object of the broadly constricted 

 basal margin of the prothorax of Deucalion, which is so regulated that it may 

 present a more perfect and contiguous surface to the mesothorax, — whilst, by 

 being more tightly draAvn as it were over that especial part, it is made likewise to 

 grate more \dgorously against the lower file. This transverse, coarctate ring is 

 not expressed at all in Borcadion, and it is but faintly suggested in a few of the 

 Parmence : so that we should a priori have expected that the stridulating power 

 of Deucalion would be more effectual than is there the case. And such, on 

 inquiry, Ave find to be a fact : for so loud is the sound which the D. Besertarum 

 is able to accomplish, that the only individual which has come mider my notice in 

 a recent state I heard at a considerable distance ; and the second example as yet 

 detected was described by the Rev. R. T. Lowe (who obtained it from the extreme 

 summit of the Ilheo Bugio, or Southern Dezerta) as emitting a " l)uzzing noise, 

 somewhat resembling that of a Humble Bee." Everything indeed in this strange 

 ffcnus seems desiijucd to c-ive full effect to these, far from umnusical, inter-thoracic 

 notes ; for, in addition to the hinder contracted belt abeady mentioned, the pro- 

 notum of Beucalion is furnished with an exceedingly deep, rounded, postmedial 

 fovea, which (since it projects beneath) must evidently form an extra instrument 

 of impact to sweep over the mesothoracic file, — when its head (and, simulta- 

 neously, its prothorax) is by turns lowered and upraised. In the Salvagian* 

 representative this impression is less developed than in the Dezertan one ; never- 



* Wliilst unwilling to insei-t the descriptions of extra-lMacloiran forms into tlio body of this work, I 

 can sec no objection to admitting the diagnoses of a few nearly allied species (both in allinity and geo- 

 graphically) into the notes. The following characters therefore of the large and remarkable Deucalion 



