1852.] '^'^ 37 



necessity of proposing important modifications of the arrangement adopted by 

 him.* 



The great increase in the number of our species, since the publication of the 

 monograph of Histers by my father,t has made me acquainted with many varia- 

 tions of structure, too unimportant to serve as foundations for separate genera, 

 yet absolutely incapable of entering any of the genera established by Erichson. 

 Some of these anomalous species have been described by me in the Annals of the 

 Lyceum of Natural History, vol. 5. 



By a careful comparison of such forms with the species to which, by obvious 

 characters, they are most nearly allied, I have been led to believe that the genera 

 in this group have been unnecessarily increased, by the use of principles of 

 division which are by no means of generic value, and which scarcely serve to 

 define small groups of species. 



I allude more especially to the structure of the tibiae, which holds so important 

 a place in the system of Erichson. The difficulty of deciding upon such an indis- 

 tinct character as the form of the tarsal groove of the anterior tibiae, and the 

 decidedly variant structure of the posterior tibiae in several of the genera, has 

 led me to reject entirely the characters drawn from those parts of the body. The 

 special variations referred to will be exposed more fully under the genera Hister 

 and Saprinus below. 



Following Erichson, I have divided the genera into three groups according to 

 the position of the head and the form of the prosternum. The genera may after- 

 wards be separated according to the following table : 



\. Caput porrectum : prosternum antice non lobatum. 



Mandibulce dentatae Hololkpta Payk. 



Mandibulae dentatae, prosternum latum planum . . iPhyllomaEf. 

 Mandibulae dentatae, prosternum elevatum, subacu- 



minatum i Oxysternus Er. 



B. Caput retractum ; prosternum antice valde lobatum. 



a. Scrobiculi antennales antici. 



1. Tarsi antici unguiculo unico i Cypturus Er. 



2. Tarsi omnes biunguiculati. 



Mandibulae porrectae, antennae sub frontis margine insertae, 



capitulo 3-articulato . . . . ^ Hister Linn. 

 Mandibulae porrectae, antennae sub frontis margine insertae, 



capitulo solido, truncato ..... sHet^erius Er. 



Mandibulae retractae, antennae in frontis margine insertae, 



capitulo 3-articulato, rotundato, .... Epierus Er. 

 Mandibulae retractae, antennae in frontis margine insertae, 



capitulo 3-articulato, truncato .... Tribalus Er. 



b. Scrobiculi antennales niedii, laterales. 



Antennae articulo Svo latiore ..... Dendrophiltts Leach. 



Antennae articulo Svo non latiore . . . Paromalus Er. 



C. Caput retractum, prosternum antice non lobatum. 



a. Antennae sub frontis margine insertae. 

 Mandibulae exsertae ; scrobiculi antennales antici . C^rosternus n. g. 



Mandibulae exsertae; scrobiculi antennales ad prosterni 



latera sit| ........ 4 Saprinus Leach. 



Mandibulae clypeo obtectae ... . . . . ^Trypon^us Er. 



* Klug's Jahrbiicher fiir Insectenkunde. 



f Boston Journal of Natural History, vol. V. p. 32. 



1 No North American species. 



2 Including Omalodes Er.; Platysoma Leach, Er: (?) Plaesius Er. and (?) Placodes Er, 

 I have not examined the last two genera, but the description furnishes no good charac- 

 ters for separating them. 



3 Hister brunnipennis Rand., and a new species. 4 Includnig Pachylopus Er. 



