DIPTERA.— TANYSTOMA. 537 
of only three joints, with a terminal seta.* The formation of their 
mouth, which is generally much exserted, is also much more perfect, 
exhibiting internally a lancet-like labrum and lingua, and a pair of 
maxillee and maxillary palpi. In the Tabanidz, moreover, the mouth 
is furnished in addition with a pair of lancet-like mandibles, at least 
in the females. In some of the Acroceridz, however, which are nearly 
allied to the Bombyliide, the mouth is nearly obsolete. 
The great character, however, by which the stirps is distinguished 
from the Notacantha and Athericera, consists in the nature of the 
metamorphosis to which all the species are subject. 
The larvee resemble worms, being nearly cylindric, without feet, 
and with a scaly head of a constant form, always furnished with un- 
guiform retractile appendages, enabling them to pierce the substances 
whence they derive their support: for the most part, they reside 
under ground, and are but little known. They shed their skin pre- 
vious to assuming the pupa state, in which, to a certain extent, they 
resemble the imago, having the various limbs enclosed in distinct 
‘sheaths, and folded upon the breast. The perfect insect escapes 
from this state by means of a slit down the back. 
Many of the perfect insects are eminently carnivorous or insecti- 
vorous. 
The following distribution of the families composing this stirps ap- 
pears to me to combine their affinities in a more natural manner than 
in the methods proposed in Latreille’s later works. It will be seen 
that it differs only in few respects from a portion of the sketch given 
by Latreille in the Genera Crust. &c. vol. iv. p. 243. n. 1. 
Section 1. ‘ Proboscis with six internal sete. (Fam. Tabanide.+) 
Section 2. Proboscis with four internal sete. 
Subsection A. Proboscis siphon-shaped ; body short, broad; wings divari- 
cating. (Fam. Bombyliide, Anthracide, and Acroceride. ) 
Subsection B. Proboscis siphon-shaped ; body long; wings incumbent. (Fam. 
Empide, Tachydromiide, Hybotid, and Asilide. ) 
Subsection C. Proboscis dilated, with two large exserted lips ; wings divari- 
eating or incumbent. (Fam. Mydaside, Therevide, Leptide, Dolichopide, 
and Scenopinide. ) 
By this arrangement of the families, Tabanus is introduced amongst 
the other groups having an incomplete pupa, instead of being united 
. 
* The Tabanidx, however, as well as the Mydaside, have no terminal seta, and 
the third joint of their antenne is articulated. 
t Latreille excepts Pangonia: it, however, certainly has six internal lancets in 
the females, although the males, as in Tabanus, &c., have only four. 
