BULLETIN 826, U. S. DEPARTMENT OF AGRICULTURE. 



A number of genera have been described which the writer has 

 been unable to place. These genera are discussed in the following 

 notes. 



Genus RHIZOBIUS Burmeister. 



1835. Rhizobius Burmeister, Handbuch der Entomolorde, p. 78. 



1849. Rhizophlhiridum Van der Hoeven, Handb. Dierkunde v. 1, p. 508. 



1860. Rh.yzok.us Passerini, Gli Afldi, p. 30. 



1863. Rizobius Passerini, Aphididae Italicae, p. 79. 



1919. Rhizoicus Del Guercio, Redia, v. 12, p. 251. 



The genus Rhizobius has generally been considered as a good 

 aphid genus and writers have referred to species in this genus as 

 having but one claw to the tarsus. However, as indicated under 

 Paracletus the writer believes this is a variable character and we 

 have no definite knowledge in regard to piloseUae Burm. Buckton's 

 species of course was not in the original genus and therefore can not 

 be used as type nor was it in Passerini' s conception of Rhyzoicus. 

 After placing Rhyzoicus Pass, with jujubae Buckton as type, Del 

 Guercio erects the genus Neorhizobius, distinguished by having two 

 claws, and in which he places graminis Thos. ? poae Del Guercio, 

 stramineus Del Guercio, and ulmiphilus Del Guercio. 



In 1860 Passerini set sonchi Pass, as the type of Rhizobius Burm., 

 and in a footnote suggested the name Rhyzoicus as a new name for 

 Rhizobius, since this name had previously been used in the Coleoptera. 

 Such procedure, however, is not allowable since sonchi Pass, was not 

 in the original genus. Of the two species in the original genus 

 pilosellae Burm. has been accepted as type. 



Del Guercio in 1917 used the generic name Rhizoicus Pass., 

 spelling it with an "i" instead of a "y", and jujubae Buckton as 

 the type. 



In the writer's opinion the genus Rhizobius must remain unknown 

 until the type species pilosellae becomes known and carefully studied. 



The name Rhizophthiridum was given to this genus to replace 

 Rhizobius Burm. 



Genus NEORHIZOBIUS Del Guercio. 

 1917. Neorhizobius Del Guercio, Redia, v. 12, p. 251. 



As indicated under the discussion of Rhizobius, four species are 

 placed in this genus by Del Guercio. Three species are described 

 as new and only in the apterous forms. 



Two of these forms have five-segmented antenna? and one of them 

 four-segmented ones, and when the alate forms are found they will 

 in all probability be shown to represent species either of Forda or 

 Geoica. The basing of genera upon the relative lengths of the 

 antenna! segments would create a very large number of genera and 

 separate related forms. The genus Neorhizobius, therefore, the 



