88 BULLETIN 826, U. S. DEPARTMENT OF AGRICULTURE, 
GENERA NOT PLACED. 
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. 
1S35. Rhizobius Burmeister, Handbuch der Entomologie, p. 78. 
1S19. RliizophtMridum Van der Hoeven, Handb. Dierkunde v. 1, p. 508. 
1S60. RJi yzoic us Passerini, Gli Afldi, p. 30. 
1863. Rizdbius Passerini, Aphididae Italicae, p. 79. 
1919. Rhizoicus Del Guercio, Redia, V. 12, p. 251. 
The genus Khizobius 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 piZoseUae 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 jufuhae Buckton as type, Del 
Guercio erects the genus Neorhizobius, distinguished by having two 
claws, and in which he places gramims Thos., poae Del Guercio, 
stramineus Del Guercio, and ulmi pJiilus Del Guercio. 
In I860 Passerini set sonclii 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 c "*y", and jujubae Buckton as 
the type. 
In the writer's opinion the genus Rhizobius must remain unknown 
until the type species pilosettae becomes known and carefully studied. 
The name Rhizophthiridum was given to this genus to replace 
Rhizobius Burm. 
Genus NEORH1ZOBIUS 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 antennae 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 
antennal segments would create a very large number of genera and 
separate related forms. The genus Neorhizobius, therefore, the 
