154 AN ACCOUNT OF BRITISH FLIES. 
segment somewhat smaller and having two black dots upon its dorsal 
surface. Several tubercles surround the base of anal segment. 
There are also two lateral tubercles on each segment, and two rows 
of four each on the ventral surface. They may be found in May 
and June under wet moss ; they turn to pupz during the latter end 
of June. 
In Scatopse the larve are fusciform, legless, as in the others, with 
two short points on the thorax at the side, and also on the eight 
abdominal segments at the base; the last segment is terminated by 
iwo divergent sete. 
The fup@ are naked, enclosed in an oval cell; thorax gibbose, 
markings of wings and legs very short, usually pale in colour (7z/- 
phus). 
The pupa of Bibio (Fig. 2, Pl. iii.) is dark brown, and has a curious 
shrivelled appearance, about one-third of an inch Jong and very broad. 
The anal segment is very small, and has two divergent spines on its 
dorsal surface. The wing cases are small and closely surround the 
legs. The thoracic portion is much elevated. The flies hatch during 
July. I have to thank Mr. Bignell for the loan of the specimens 
figured. 
Their range in space is wide; they occur abundantly from Scandi- 
navia to the tropics, and in America they appear in great numbers, 
and do considerable damage to crops. Their geological range 
is limited, but no insects occur so abundantly in a fossil con- 
dition as the Azbionide.* They appear first in the tertiary beds ; 
there are records of their appearance in the mesozoic, but the species 
are very doubtful, and we cannot place the true record of their 
appearance further back than the tertiary period. But in the tertiary 
epoch they are the most abundant insects ; they are not, however, 
' rich in species, but what do occur are found in great numbers. They 
are rare in amber. Loew found the genera Diélophus, Plecia and 
Scatopse ; Bibio is strangely enough wanting. P/ecia also occurs 
abundantly in the rock formations in Aix, Oenigen, Auvergne, Wyom- 
ing, etc. 42bi0 occurs most abundantly in the rocks, between forty and 
fifty species have been described from various places in Europe and 
America. There seem to be some extinct genera found, such as 
Epiplecia, Siard, which occurs at Covent; also Protomyia and Bibi- 
opsis, genera formed by Heer, but which are considered by Loew not 
* Note sur les Bibionides fossilis. Bull. Sc. dép. Nord. T. i., Lille, 1878; also 
Bibioniden aus der rheinischen Braunkohle Von. Rott. Pal. Band. Siard. xiv. Taf. 
8 and 9, 1865. Heyden, etc. 
