COLLEMBOLA OF THE FAMILY ISOTOMIDAE O 



pointed olfactory setae, as in Achorutes. The manubrium is naked 

 ventrally. The dentes are subcylindrical and in antiqua apically 

 rounded; dorsally they are tuberculate, but the tubercles are not 

 different from those of the rest of the integument. The mucrones, 

 with an apical tooth, an anteapical tooth, and equal outer and inner 

 lamellae, are essentially like those of some species of Achorutes. Those 

 of antiqua and muskegis are remarkably like those of Achorutes socialis 

 Uzel. The pigment is dark blue. 



The three species of Guthriella belong, however, in the family 

 Isotomidae. The postantennal organ is externally a single tubercle, 

 elliptical in contour, and in muskegis with an anterior notch like that 

 in many species of Proisotoma. The furcula arises apparently from 

 the fifth abdominal segment. The body has no intersegments. The 

 pro thorax and anal segment are relatively shorter than in Achoru- 

 tinae. Anal spines are absent. The tibiotarsus has a distal subseg- 

 ment. The claws are isotomid in type. The unguiculus has a pair 

 of inner lamellae. The manubrium is relatively slender. The body 

 setae are more nmnerous than in Achorutinae. 



The species of Guthriella have near the base of the furcula a pecuhar 

 lateral suboval sclerite, the homolog of which I have not found as yet 

 in Poduridae. 



The primitive genus Guthriella leads into Proisotoma through the 

 subgenus Ballistura. Linnaniemi (1912) rejected Ballistura as being 

 an unnatural group, but I find it a convenient group to use for a few 

 species in this country and in Europe as well, even though it does 

 intergrade with Proisotoma. The species of Ballistura, typified by 

 B. schotti Dalla Torre, have for the most part the same characters 

 as Guthriella, but differ from that genus in having flatter body seg- 

 ments, wide intersegmental membranes, and imbricate tergites, with 

 a smooth integument; while the dentes are dorsally smooth or have 

 a relatively few rounded lobes. 



Archisotoma is an aberrant genus, the single species of which 

 resembles Ballistura, especially in the form of the third urotergite and 

 in the characters of the manubrium and dentes. 



The monotypic genus Agrenia has a few of the characters of Iso- 

 toma, but it is closer to Proisotoma on account of its simple third 

 urotergite, stout tuberculate dentes, lamellate mucrones, and short 

 body setae. 



Proisotoma schafferi and P. rainieri are also related to Ballistura. 



Most of the species of Proisotoma are referable without difficulty 

 to that genus; the few that are not are the species that connect 

 Proisotoma with Isotoma. 



Ankylosis of the genital and anal segments occurs in many species 

 that are in other respects dissimilar. Hence the subgenus Isotomina, 

 based solely upon that character, is too unnatural to be used. Its 



