Insect a. 223 



whole are relatively longer tlian in /. silvatica, while in the latter 

 species the third and fourth abdominal segments are equal to one 

 another, and the mucro is comparatively short and stout. It could, 

 however, be readily derived from the mucro of /. Klovstacli, as the 

 general arrangement of the teeth is identical in the two species. 

 The post-antennal organ in /. silvatica is more rotund than in 

 our insect. 



Several of the specimens were so mounted as to exhibit portions 

 of the jaws. It seemed advisable, therefore, to figure the parts 

 visible — the labium (Fig. 3) and the extremity of a maxilla and its 

 palp (Fig. 2). The maxillary palp in this species is prolonged into 

 a thin leaf-like process bearing four bristles, while the fifth bristle 

 is borne on a very prominent papilla. 



Our knowledge of the distribution of these insects is as yet too 

 incomplete to elucidate any details of ancient geography. But the 

 existence of a species of this order of wingless insects in Geikie Land 

 — a species belonging to a genus widely spread in the northern 

 hemisphere— cannot but support the theory of a former extension of 

 the Antarctic Continent. And the further fact that the species is 

 closely related to a Fuegia;n insect is consistent with the view that 

 there may have been a southern route of migration between eastern 

 and western lands. 



EXPLANATION OF FIGURES. 



Plate XL VII. 



Fig. 1. — Isotoma Klovstadi. Dorsal view, x 18. 



Fig. 2. — Left maxilla (ventral aspect), showing head and extremity of pali>, x 350. 



Fig. 3. — Labium (ventral aspect), X 350. 



Fig, 4. — Ocelli and ])ost-antennal organ of right side, x 200. 



Fig. 5.— Fore-foot, x 350. 



Fig. 6.— Hind-foot, x 350. 



Figs. 7, 8. — ^lucro drawn from two specimens to show variation, x 350. 



