Iv. Jordan and N. 0. Rothschild 
23 
They are, however, of some morphological interest and frequently offer 
characters of taxonomic value. The hinder portion of the head (ox- 
occiput) bears normally in fleas three rows of bi-istles, one near the base 
of the antenna, a second in the centre and a third near the hinder edge 
of the head. It is interesting to find that these three rows are 
continued also over the frontal pox-tion of the head (PI. II, fig. 3). Here 
the anterior row extends from the maxillary palpus to the base of the 
antenna, the second row is placed in front of the eye, consisting usually 
of three long bristles, while the third row, which is absent from most 
fleas, is situated on the genal process. The three rows divide the head 
in four sections, cox-responding pei-haps to the four segments of which 
the head is composed. 
The thorax of the Siphonaptera has some vex-y chai-actei’istic 
featux-es. The three segments (pro-, meso- and metathorax) are each 
quite distinct, while the incision, however, between the px-o- and 
mesothorax is deep, the meso- and metathorax are more closely applied 
to each othei-. The thorax therefore in this l-espect resembles most 
nearly that of Coleoptera, with this difference, that in Siphonaptera the 
hind edge of the xxxesonotxxm is similar to the metanotum and ovei’laps 
the same, and the nxetasternite projects farther ventrad than the 
mesosternite, the two segments not being 'so closely connected as ixx 
Coleoptera and Rhynchota. Each of the three thoracic tergites of 
Siphonaptera forms a simple half-ring, there being no distinct division 
—by a suture—into two principal sclei’ites, a scutellum and a post- 
scutellum, as in other holometabolous insects. In Loemopsylla the 
tergites ai-e narrow and bear each only one single row of bristles, as is 
also the case in Pulex, Ctenocephalus, and some other allied genera 
(PI. I). In the </ of Loemopsylla . regis, however, there are doi-sally 
a few hairs in front of this row on the pro- and mesonotum. This 
single row corresponds to the postmedian row of bristles of other 
fleas, the bristles of this row being always longer than those of 
the preceding row or rows. The width of the segments of the 
thorax varies to a slight extent in Loemopsylla, the mesonotum 
especially being distinctly longer in some species than in others. The 
comparatively long mesonotum of the heavy-spined Loemopsylla 
chephrenis Rothsch., and the likewise comparatively long metanotum of 
the long-bristled Loemopsylla longispinus Wagn., have only one row of 
bristles, while in some American allies of Loemopsylla these tergites, 
which have no greater width than in the Loemopsylla mentioned, bear 
two or even thx-ee i-ows of bristles. From this it is obvious that the 
