20 
The Non-Combecl Eyed Siphonaptera 
the majority of fleas, the tip of the segment being more or less sym¬ 
metrical (PI. II, fig. 9). In other forms one or two bristles on one or both 
sides are lost, while in the Sarcopsyllidae all these bristles are absent. 
The non-combed fleas from the Old World, allied to Pulex, differ widely 
in respect to these bristles from those found in America. In Rhopalo- 
psyllus and the allied genera from America described hereafter the end 
of the rostrum is practically symmetrical with six bristles at the tip of each 
end-segment (PI. II, fig. 9). These Pulicidae , therefore, have preserved 
the tip of the rostrum in a generalized state of development. On the 
other hand, in the Old World non-combed fleas, with the exception of 
lamellifer, the end-segment of each labial palpus is obliquely truncate, 
being asymmetrical and bearing only three bristles at the edge (PI. II, 
figs. 3, 10, 11). The same very striking characteristic obtains also in 
Ctenocephcilus and Spilopsyllus, which are close allies of Pulex and 
Loemopsylla. 
Some further peculiarities which separate the Old World allies of 
Pulex from the New World genera are the shape and structure of the 
prae-antennal or frontal portion of the caputal capsule. A large number 
of fleas possess the so-called frontal tubercle or notch in the centre of 
the frons, but nearer to the mouth than to the antenna. This tubercle 
is especially well developed in nearly all the species of Geratophyllus and 
allied genera, being sometimes inserted in a groove. It attains its 
greatest development in Listropsylla agrippinae Rothsch. (1904 a, p. 634), 
and in this species is heart-shaped (or rather, like the “spade” in cards) 
and projects from a groove. The real nature of this organ is at present 
unknown, though presumably an organ of sense, and its homology is also 
uncertain. The organ is suggestive of the egg-breaker of the larva, but 
is probably a new acquirement, being perhaps neither a modification of 
some organ possessed by the ancestral Siphonaptera ( ocellus , for instance), 
nor a remnant from the larval stage. The simple tubercle of many 
Geratophyllus may not however be homologous to the tubercle placed in 
a groove, but in any case the organ is of considerable taxonomic value 
in those Pulicidae we are here dealing with. This tubercle situated in 
a groove is well developed in all the American forms, but is not met with 
in any species of the Old World genera Pulex, Pariodontis, Moeopsylla 
and Loemopsylla. In Moeopsylla only there is a minute tubercle, which 
is not however situated in a groove and is placed much more dorsal 
than in the American species. 
A second characteristic feature in the prae-antennal portion of the 
head of Loemopsylla and its allies obtains in the development of the 
