256 INSECT A. 



These Insects run with great velocity; some of them by means of 

 their caudal appendages are enabled to leap. They are divided into 

 two subgenera. 



Machilis, Lat. Petrobius, Leach. 



Eyes very compound, almost contiguous, and occupying the greater 

 part of the head; body convex and arcuated above; abdomen termi- 

 nated by small threads for saltation, of which the middle one, placed 

 above the two others, is much the longest. 



The maxillary palpi are very large, and have the form of small 

 feet. The thorax is strangulated, the first segment smaller than the 

 second and arched. 



These Insects leap well and frequent stony and enclosed places. 

 All the species known belong to Europe(l). 



Lepisma, Lin. Forbicina, Geoff., Leach. 



Eyes very small, widely separated, and composed of a small num- 

 ber of granules; body flattened, and terminated by three threads of 

 equal length, inserted on the same line, and of no use in leaping. 



Their coxae are very large. Most of the species inhabit the inte- 

 rior of houses. 



L. saccharina; Forbicine plate, Geoff., Insect., II, xx, 3; 

 Schseff., Elem. En torn., lxxv. Four lines in length; of a silvery 

 and somewhat leaden hue and immaculate; originally, it is said, 

 from America, now very common in houses in Europe. 



L. vittata, Fab. Body cinereous, dotted with blackish; four 

 streaks of the same colour along the back of the abdomen. 

 Other species are found under stones. 



FAMILY II. 



PODURELL.E, Lat. 



Antennae quadriarticulated ; no distinct or salient palpi ; 

 abdomen terminated by a forked tail folded under the venter 

 when at rest, and used for leaping. The Podurellse form but 

 one genus in the Linnaean system. 



(1) Lepisma polypodia, L.; L._ saccharina, Vill., Entom. Lin., IV, xi, I; Koem. 

 Gener. Insect., XXIX, I; Forbicine cylindrique, Geoff.; Lepisma themana, Fab.; 

 Petrobius maritimus, Leach, Zool. Miscell., CXLV. 



