ARTICULATA. 145 



Latreille in 1796, and considered a tribe of his order Gymnognatim by 

 Burmeister, the body is apterous, more or less cylindrical, and often covered 

 with minute scales like a silvery dust. The antennte are longer than the 

 head, and the mouth is provided with mandibles and maxillae. They are of 

 active habits, living in woods, among moss, or beneath stones and bark. 

 Some of the small species are sometimes found on the surface of the water 

 near the margin, or hopping about on the surface of snow in winter, some- 

 times in great numbers. The order contains the two families, Podaridai 

 and LepismidcG. 



Fam. 1 PodxiridcB. Here the body is oblong or globular, the antennte 

 are rarely composed of more than four articulations, but in the genus 

 Macrotoma the three or four articulations are divided into a great many 

 rings or indistinct segments, indicating an affinity with the Lepismidge. 

 The palpi are indistinct according to some authors, and absent according to 

 others. The mandibles and maxillse are membranaceous, the eyes simple, 

 varying in number, and the abdomen is four or six articulate. The pro- 

 thorax is sometimes much reduced in size, or w\anting above, although a 

 part of it remains below, to which the anterior feet are attached. The 

 posterior extremity is provided with a spring or appendage bent along the 

 abdomen, and used in leaping. This, however, is wanting in the genus 

 Anura, in which the mandibles and maxillae seem to be absent. They 

 are usually confined to damp places, and die very soon if deprived of 

 moisture. The oral aperture is so minute that it is supposed they subsist 

 upon the juices of decaying vegetable matter. 



Podura {pi. 77, fig. 79 «, natural size ; 5, magnified, exhibiting the 

 caudal spring). Smynthurus {fig. 80) has the abdomen large and globular. 

 The species of this genus are often seen hopping upon the surface of water 

 and snow. The dark-colored species of this family are so abundant at 

 times as to give the snow the appearance of being sprinkled with course 

 gunpowder. J. M. M'Minn mentions their occurrence in the mountains of 

 Pennsylvania, in the following words (Proceed. Acad. Nat. Sei. iv. 246) : 

 " I have frequently noticed them in mid-winter on the snow, but I never 

 saw such a multitude of them together as I witnessed on the 17th of 

 Feb., 1849. The snow was entirely covered for the fourth of a mile along 

 the road, and several rods on either side. The mercury in Fahrenheit was 

 standing about fifteen degrees ; the atmosphere was dry and clear. These 

 little animals were quite stupid, and to all appearance had been but a short 

 time there, and as it was about nine o'clock in the morning, I judged that 

 they arrived at night. Their motion was slow, and those on the top were 

 quietly endeavoring to get under. The next day, when I again jjassed the 

 spot, I could not detect a vestige of them. The wind had been strong from 

 the north for several days, and I have noticed that we had strong north 

 winds whenever I had seen them." This species is j^robably the Podura 

 nivicola described by Dr. A. Fitch, who gives a similar history of it in his 

 account of the " Winter Insects of Eastern New York," published in the 

 Am. Jour, of Agr. and Sei. for May, 1847. 



Fam. 2. Lepismidce. In this family the antenna are setaceous, and 



349 



