K. Jordan and N. C. Rothschild 
7 
psyllidae. The three free processes of the clasper are found in several 
of the old-world genera of the Pulicidae, the main characteristic, however, 
exhibited by P. irritans and the Sarcopsyllidae, i.e. that the second and 
third processes form a kind of claw, is not found in any of the other 
species. The genitalia of P. irritans are probably of a more primitive 
type than the genitalia of any other Siphonaptera (see Jordan and 
Rothschild, 1906, p. 38). Pidex irritans exhibits a further distinguishing 
character in the position of the bristles on the head, the bristle situated 
in front of the eye in most species being absent in irritans and replaced 
by one below the eye, as is also the case in Loemopsylla ehephrenis. 
The hindcoxa—as is the case in some species of the genus Loemopsylla 
—is pear-shaped, but in Pidex irritans this coxa can be distinguished 
from that of any other known flea by bearing a number of hairs 
situated on the inner surface of the posterior (= meral) portion. A most 
interesting feature in the morphology of this flea is the presence in 
a large proportion of specimens of both sexes of a small tooth at the 
genal edge of the head, slightly behind the lower oral corner. This 
tooth from its position and structure corresponds to the fifth tooth of 
the genal comb of Ctenocephalus canis and allies. This single small 
tooth of P. irritans (often absent) is the last remnant of the genal comb 
with which, we think, the ancestral forms of irritans were provided. In 
the case of Ctenocephalus erinacei the teeth of both the genal and the 
prothoracic combs are small in size and few in number and occasionally 
almost disappear. This fact seems to us to be further evidence that 
the ancestral forms of P. irritans possessed both genal and prothoracic 
combs. 
1. Pulex irritans Linnaeus (1758). 
Pidex, Puce, Floh, Flea, etc., Moscketti (1544) ; Schwenckfeld (1603, p. 550) ; 
Hooke (1665, p. 61, t. 32, ^) ; Borrich (1676, p. 185) ; Charleton (1677, p. 53) ; 
Muralto (1682, p. 137); Griendel von Ach (1687, p. 17, fig. 4) ; Bonarmi (1691, 
fig. 56) ; Leeuwenhoek (1695, p. 20) ; Leeuwenhoek (1698, p. 325, fig. 1-20) ; 
Cestone (1699, p. 42, fig.); Leeuwenhoek (1706, p. 2311, proboscis); Bonanni 
(1709, p. 345, t. 377, fig. 49, t. 378, fig. 50-56); Camerarius (1714, p. 71); 
Joblot (1718, t. 13, fig. 6) ; Vallisnieri (1733, t. 25, fig. 1) ; Frisch (1734, p. 8) ; 
Cuno (1734); Bertolotto (1834); Albin (1736, p. 69, t. 41, $ ) ; Linnaeus (1744, 
p. 96); Adams (1743-46, t. 27); Rosel (1749, p. 10, t. 4, fig. 26, partim, 
good descr. of life-hist, of dog-flea) ; Linnaeus (1748, p. 67) ; Baker (1753, 
t. 13, fig. 6) ; Linnaeus (1756, pi. 73) ; Kniphof (1759, § 15); Ledermiiller (1761, 
pi. 41, t. 20, $, metamorphosis); Geoffroy (1762, pi. 616, t. 20, fig. 4, $); Weiss 
(1762, p. 340) ; Yeats (1773, p. 243); Degeer (1778, pi. 7, t. 1, fig. 1); Martynn 
(1785); Ray (1788, pi. 483); Latreille (1796, pi. 172) ; Fitzgerald (18—?, pi. 268, 
