278 Journal New York Entomological Society, t^'o'- xxiv. 



uropods of the third abdominal segment form the tenacukim, when 

 present, and those of the fourth or fifth abdominal segment form the 

 springing apparatus (furcula) when present. Mouthparts retracted 

 in cavity of head. Labial palpi wanting. Postantennal organ usually 

 present. Eyes present or absent. Antennae usually four- to six- 

 segmented. Head rounded and directed straight forward (prog- 

 nathous) or obliquely downward. Body comparatively long, and the 

 abdomen sub-cylindrical. Abdominal segments, which do not exceed 

 six in number, usually free or distinct (whence the name Euarthrura). 

 There is no postembryonic increase in the number of abdominal 

 segments. Abdominal ganglia wanting, or united with the last 

 thoracic ganglion. Heart with six pairs of ostia. The principal 

 families of the group are the Achorutidse and Entomobryid?e. 



If the preceding group be regarded as of the value of an order, 

 it might be divided into two suborders as follows: (a) The " Eupo- 

 dura," including those forms in which the springing apparatus is 

 usually well developed, and is generally attached to the penultimate 

 segment (although in some Isotomas it is attached to the antepen- 

 ultimate segment). The head is directed obliquely downward, and 

 scales usually occur on members of this subdivision. Examples are 

 Isotoma, Orchesella, etc. (&) The " Patiropodura," including those 

 forms in which the springing apparatus is reduced or wanting, and 

 when present is attached to the antepenultimate instead of to the 

 penultimate segment. The head is directed straight forward, the 

 body is usually granular, and scales are absent. Examples are 

 Podura, Achorntes, Amirida, Ncanura, etc. 



3. Sminthuroides (Synarthrura). — Styli absent. Segmented 

 cerci, or forceps-like terminal abdominal appendages wanting. Uro- 

 pods of first abdominal segment more or less grown together and 

 modified to form the ventral tube, whose vesicles may be long and 

 tubular, or short and sac-like. Springing apparatus usually present. 

 Mouthparts retracted in cavity of head; Labial palpi wanting. 

 Postantennal organ usually absent. AntemicC, with few exceptions, 

 elbowed and four-segmented. Head rounded and usually vertical in 

 position (z. e., directed downward). Body short and abdomen sub- 

 globular. Thoracic and abdominal segments more or less closely 

 united (whence the name "Synarthrura"). No postembryonic in- 

 crease in the number of abdominal segments. Abdominal ganglia 



