54 FAMILIES OF PETALOCERA WHICH LIVE 



articulum secundum productis, paululum extus 

 arcualis, fimbriatis. 



Mentum crustaceum, subquadratum, profundi emargina* 

 turn. 



Caput subsemicirculare ; clypeo sccpe dentato, internum 

 cornuto. Corpus orbiculato-omle, convexum vel 

 depressum; abdomine brevi, elytris haud obtecto. 

 Thorax transversus ; scutello rarissime distincto, 

 subtrigono. Pectus magnum, ideoque femora 

 intermedia ad basin latl dispartita. Pedes va- 

 lidi, unguibus minimis ; tibia antica extrinsecus 

 o-dentata, apice calcare uno instructs, tarsis 

 exiguis, in quibusdam obsoletis ; tibia media 

 apice Q-calcarata, postice calcare uno instructs. 



Observations. 

 The Scarabaida occupy a most important place in the 

 economy of nature, and possess so very distinct a form 

 that they are only likely to be confounded with the Apho- 

 diida ; from these, however, they may be distinguished by 

 their elongate lanceolate mandibles and large pectus. 

 Several genera of the Scarabaida, — such as Onitis, Ontho- 

 phagus, &c. — approach so nearly to Aphodius, that here, 

 as in most cases where families meet, it will be found most 

 difficult if not impossible to draw the line of demarcation. 

 There is less likelihood of confounding them with the 

 Geotrupida, because, though several insects in both fami- 

 lies evidently approach to one another in general form and 

 structure, yet none that I have yet seen can accurately be 

 said to fill up the interval that occurs between the cor- 

 neous porrect mandibles of the one family, and those. 



