536 MODERN CLASSIFICATION OF INSECTS. 
M. Van Roser having described and communicated to me those of Xyl. 
ater Meig.* The larva (fig. 127. 18.) of this insect + is an apod fleshy 
grub, of a somewhat cylindric form, having the tail defended by an 
oblique scaly plate, terminategs by two short obtuse scaly horns (/ig- 
127. 19. sideways), whilst the anterior extremity of the body is termi- 
nated by along acute horny joint. The structure of this larva is not 
that of a species having a coarctate pupa, and I am consequently thence 
led to infer the direct relation of Xylophagus with Pachystomus {, in 
a family distinct from that which contains Subula, although the only 
appreciable difference between Xylophagus and Subula consists in a 
slight variation in the direction of one of the veins of the wings. 
For the family thus constructed of Canomyia, Pachystomus, and Xy- 
lophagus, I should have retained the name of Xylophagide, had not that 
name been used in a different extent by other authors, the retention of 
which would therefore have led to confusion. The mouth of Czno- 
myia (the only genus yet examined in respect to its oral characters, 
Jig. 127.15.) has the labrum, lingua, maxillze, and palpi fully developed, 
and thus resembles the majority of the Tanystoma. The apex of the 
abdomen in the females is produced into a long, and often exserted 
ovipositor. Of the relations of these insects with the other Diptera, 
we thus see that in regard to their trophi and transformations, the 
Caenomyide in fact belong to the Tanystoma, whilst their close re- 
lation to Subula and other Notacantha has already been shown. Hence 
I cannot adopt the situation assigned to them by Macquart, Meigen, 
&c. immediately succeeding the Nemocera. 

The insects composing the third stirps of the order Diptera, or the 
Tanystoma Laér., are distinguished by having the antenna composed 
* M. Van Roser (Verz. Wurt. Dipt. p. 6.) notices the great difference between 
this larva (which he found in decayed birch-wood) and that of Subula varia, but 
without describing it. Baumhauer also found the larva of this insect in rotten 
wood, but did not describe it. 
+ The larva figured by Réaumur (Mém. tom. iv. pl. 13. f. 12-16.) evidently 
belongs to this or a closely-allied species. 
{ Meigen indeed gives them as congeneric, regarding P. syrphoides as identical 
with X. cinctus De Geer; whilst Fallen even makes this last a variety of Xylo- 
phagus ater. Macquart, however, states them to be generically distinct, and places 
them in distinet tribes; which is certainly unnatural, now that their transformations 
are known. 
