392 INSECTS. DIPTEEA. 



of which the last is large, triangular, but rounded exteriorly ; 

 eyes slightly projecting, granular ; thorax flat and semicir- 

 cular, middle of the back with a longitudinal cavity termi- 

 nating posteriorly in an elevation ; abdomen ovoid or oval, 

 with from six to eight segments ; feet inserted high on the 

 thorax, with a cavity on each side between the first and se- 

 cond pairs for the admission of air. 



N. Blainmllii, Lat. (Phthiridium, Leach.) Deep chestnut brown, 

 with the feet paler ; thighs and legs almost cylindrical ; under 

 part of the thorax granulated, with two rows of long teeth at its 

 upper and lateral extremity. 2 lines long. Inhabits Isle of France. 

 Nouv. Diet. xiii. 133. 



N. vespertilionis, Lat. Upper part of the body and feet reddish 

 yellow ; below the thorax of a reddish brown, with a black line 

 in the middle ; thighs and legs much compressed, almost ellipti- 

 cal, the two rows of teeth on the lateral and upper extremity 

 of the thorax short. Inhabits Europe, on the horse-shoe Bat 

 Leach, Zool. Mis. iii. pi. 144. 



Fossil Insects were arranged by Linnaeus under the term 

 JEntomolithus, which was applied to petrifactions including 

 vestiges of insects and the Crustacea. The remains of true 

 insects found in a fossil state are few in number, and are met 

 with only in the later alluvial formations. Of those found in 

 amber a good many species have been determined ; but all of 

 genera peculiar to the countries where this substance occurs. 

 The amber itself, being chiefly found in beds of fossil wood or 

 lignite, may have had a similar origin with the copal amber 

 which exudes from the Valeria Indica of Linnaeus when cut, 

 and which while fluid envelopes the insects which happen to 

 alight on it. The insects inclosed in the amber collected on 

 the coasts of the Baltic sea were found by Latreille not to be 

 penetrated by that substance ; but that in all cases where the 

 animal was of medium size the body was always hollow. The 

 irregular position of these insects in the amber corresponds ex- 

 actly to what is observed when a fly falls into a fluid of the 

 consistence of syrup or liquid gum. The comparatively recent 

 envelopement of insects in amber is further corroborated by the 

 amber of different localities inclosing only insects proper to that 

 geographical range ; and the beds of fossil wood which accom- 

 pany the presence of this substance, have been conceived to be of 

 a structure corresponding to that of trees producing resin. 



