[93] APTERYGOTA 91 



1 1 ; basal segment stout, cylindrical ; second cylindrical ; third cla- 

 vate, apically constricted; fourth subclavate, apically rounded. Body 

 elongate ; segments in relative lengths as 2:6:6:5:6:6:5:3:2. 

 Superior claws (fig. 38) slightly tapering, feebly curved, inner margin 

 excavated, untoothed ; inferior claws two-thirds as long, broadly lan- 

 ceolate, acute, with a longitudinal rib parallel with the inner margin ; 

 tenent hairs absent. Furcula appended to the fourth abdominal seg- 

 ment, short, not attaining the ventral tube; dentes nearly twice the 

 manubrium in length, slender, uniformly tapering; rau crones (fig. 39 ) 

 slender, conspicuously bidentate ; apical tooth slightly hooked, second 

 tooth larger, erect. Clothing of numerous short setae of two kinds, 

 stiff or curving, becoming longer toward the apex of the abdomen. 

 Length 1.6 mm. 



Two specimens, Sitka, June, 1899 (No. 71). 



The Alaska specimens agree with European examples of the species 

 which I received from Dr. Schaffer, except in having stouter claws 

 and antennae and in being rather larger. There is less agreement with 

 specimens from Massachusetts, as the antennae of the Alaskan forms 

 are shorter as compared with them, the claws stouter and the mucrones 

 more slender, with subequal teeth ; moreover, the fourth abdominal 

 segment, shorter than the third in the latter specimens, is twice as long 

 as the third in the Harriman examples. 



Isotoma Jitnetaria, well known in northern and middle Europe, is 

 also widely distributed through the Arctic regions, as the above list 

 shows. The species doubtless occurs extensively in the United States 

 also, being recorded from California and having been found by myself 

 in Massachusetts and Ohio. 



ISOTOMA VIRIDIS Bourl. 

 (PI. iv, fig. 4, type.) 



? Podura viridis MiJLLER, Zoologiae Danicae Prodromus, p. 183, 1776 (Den- 

 mark). — PGmelin, in Linne Systema Naturae, Ed. 13, p. 2910, 1788. 



Podura viridis Bourlet, Memoire Podurelles, p. 24, 1843 (France). 



? Podura plumbea Muller, Zoologiae Danicae Prodromus, p. 183, 1776. — • 

 ?0. Fabricius, Fauna Groenlandica, p. 211, 1780 (Greenland). 



Isotoma viridis Bourlet, Mem. soc. sc. agric. arts Lille, Pt. 1, p. 40 r, 

 1839 (France). — Gervais, in Walckenaer, Hist. nat. ins. apt., in, p. 433, 

 1844. — Lubbock, Monograph Coll. and Thys., p. 169, 1873 (England). 

 — Parona, Saggio Catalogo Pod. Ital., p. 42, 1878 (Italy) ; Ann. mus. 

 civ. st. nat. Genova, xviii, p. 463, 1883. — Reuter, Ofv. finsk. vet. soc. 

 forh., xxxill, p. 229, 1 89 1 (Siberia). — Schott, K. sven. vet. Akad. 

 hand., xxv, No. II, pp. 59-61, taf. 5, figs. 1-5 ; taf. 6, figs. 1, 2, 1894 



