COLLEMBOLA OF THE FAMILY ISOTOMIDAE 7 



DEFINITIONS 



The expression ''Haut gefeldert" I have translated as "integument 

 reticulate." Borner (1901b, 1902a) called attention to this Idnd of 

 integument, which is smooth externally but with an underlying net- 

 work dividing the integument mto minute polygonal areas (pi. 22, 

 figs. 236, 237). It is characteristic of Anurophorus, Tetracanthella, 

 and Uzelia and occurs also in three of our species of Proisotoma, 

 namely, titusi, vesiculata, and bulbosa. In the last-named species 

 the integument is minutely tuberculate, becoming smooth and reticu- 

 late on the posterior regions of the body segments and on the inter- 

 segmental membranes. 



The term "urotergite" refers to the tergite of an abdominal seg- 

 ment, following Packard, who designated the abdominal segments of 

 arthropods as "uromeres." 



Frequently the furcula apparently arises from the fifth uromere, 

 but morphologically it always belongs to the fourth, as Willem (1900) 

 showed. 



In the descriptions of mucrones the teeth are numbered in the order 

 that happens to be most convenient, without strict regard to their 

 theoretical evolutionary sequence. 



The relative lengths of the antennal segments vary in different 

 individuals of the same species and in different instars of the same indi- 

 vidual to such an extent that the antennal ratios given in this bulletin 

 are only close approximations. 



Family ISOTOMIDAE Borner 



Isotominae Schaffer, 1896, p. 179.— Borner, 1903, p. 170; 1906, p. 160. 

 Isotomini Borner, 1901a, p. 43; 1901b, p. 14. 

 Isotomidae Borner, 1913a, p. 319. 



Pronotum membranous and without setae (except in Guthriella). 

 Mesonotum not projecting over the head. Third and fourth uroter- 

 gites approximately equal in length, or the fourth longer than the 

 third; one being never more than one and one-half times as long as 

 the other. Last two or last three abdominal segments sometimes 

 ankyiosed. Postantennal organs almost invariably present, each 

 consisting externally of a simple tubercle. Antennae 4-segmented, 

 relatively short. Trochanteral organ absent. Tarsi with one or two 

 claws. Inner edge of unguis alwaj^s simple, never basally split or 

 doubled. Furcula present (except in Anurophorus and its allies), 

 often appended apparently to the fifth abdominal segment. Manu- 

 brium seldom naked ventraUy, but with setae. General clothing of 

 simple setae, the largest of which are sometimes serrate or fringed, 

 but never clavate and fringed on aU sides. Integument smooth and 

 with sclerites, except in achorutoid species, in which it may be 

 tuberculate and without definite sclerites. Scales absent. 



