12 PROC. ENT. SOC. WASH., VOL. 24, NO. 1, JAN., 1922 



EXTERNAL ANATOMY OF THE ELATERID GENUS MELANOTUS 



(COLEOP.) WITH REMARKS ON THE TAXONOMIC 



VALUE OF CERTAIN CHARACTERS. 1 



Bv R. H. VAN ZWALUWENBURG. 



In the following study of the general external anatomy of 

 the Melanotus adult, discussion is confined to American repre- 

 sentatives of the genus, and detailed descriptions are drawn 

 either from M. fissilis Say or M. communis Gyllenhal, both 

 widely distributed species throughout the eastern United 

 States. Throughout the genus, as far as the writer has ex- 

 amined, there is a great uniformity in the general anatomical 

 features. 



Form elongate; unicolorous (only leonardi Leconte and 

 taenicollis Leconte are bicolored); varying with the species 

 from yellowish brown to black; size varies from less than 

 5 mm. (insipiens Say) to more than 18 mm. (9 decumanus 

 Erichson). 



HEAD. (M. fissilis Say, fig. 1.) Oval in outline as seen 

 from above, with eyes somewhat protruding. Occipital fora- 

 men higher than wide, its lateral margins slightly converging; 

 the superior margin (Spm, fig. 1) regularly curved on its median 

 portion with its sides oblique and nearly straight to the lateral 

 margins; inferior margin sinuate between the gular sutures 

 (fig. 2). Lateral and superior margins with a finely rounded 

 carina. 



Throughout the genus a heavy carina (shown in fig. 2 in 

 profile at the posterior margin of the eye) arises on the anterior 

 end of the gena near the mandible, and extends backward and 

 upward at a varying distance from the margin of the eye; it 

 is most strongly pronounced along the basal third of the eye, 

 less so on the upper part of the gena, and finally (in fissilis 

 Say) ending in a more or less distinct, impressed line on the 

 occiput, varying somewhat in length but usually extending 

 about halfway along the inner margin of the eye. and parallel 

 with it. 



The occiput in fissilis Say is finely and closely punctate; the 

 upper part of the gena impunctate and shiny. Across the 

 epicranium a sudden transverse coarsening of the punctuation 

 to a widely umbilicate character marks the approximate 

 position of the anterior margin of the pronotum in the undis- 

 sected insect. Anteriorly and ventrally the gena is narrowed 

 between the maxilla and the eye to the inferior basal margin 

 of the mandible (fig. 2). 



'Note. The writer is indebted to Dr. A. G. Boving, Dr. G. C. Crampton, 

 Mr. J. A. Hyslop and Mr. R. E. Snodgrass for reading the manuscript and 

 offering valuable suggestions, and to Mr. K. M. King for verifying some of 

 the details in the drawings. 



