1905-6.] Collembola from the South Orkney Islands. 477 
of Danco Land and the neighbouring islands.* The present species 
from the South Orkneys is very closely related to Willem’s insect, 
differing chiefly in having only twelve ocelli (instead of fourteen), 
and in the comparatively short and stout mucro of its spring. In 
the adult C. crassus the six ocelli on either side are arranged in 
an anterior triangular group of three and a posterior curved row of 
three (fig. 16), (the fourth ocellus, nearest to the centre of the head, 
which is present in C. antarcticus, being here absent). In the 
very young C. crassus the six ocelli are more closely grouped 
(fig. 15). These very young individuals (fig. 13), only *5 mm. in 
length, have the violet pigment mottled over their bodies, contrast- 
ing strongly with their almost black parents. The springs of 
these young — especially the dentes and mucrones — are shorter and 
stouter than those of the adults (figs. 21, 22, 23). Among the adults 
the males may be distinguished from the females (fig. 14) by 
their more slender form and more elongate feelers (fig. 16). In 
the male these have the terminal segment half as long again as 
the third, while in the female there is no appreciable difference in 
length. The antennal organ consists of a single papilla at the 
extreme tip of the terminal antennal segment (fig. 16, a. o.).f 
In the excessive reduction of the hindmost abdominal segment 
(fig. 14, abd. vi.), retracted and almost hidden in a depression of the 
genital segment (fig. 14, abd. v.), C. crassus agrees closely with 
G. antarcticus as described and figured by Willem. This character 
gives the name to the genus. 
Examination of the mouth-parts of C. crassus (figs. 18-20) shows 
that they conform to the type usual in the Collembola. The 
mandible is very slender at the tip, which bends markedly towards 
the centre of the head (fig. 18, ap.) and ventralwards (fig. 20); 
the apical teeth are feeble and close together. On the outer edge 
of the mandible, opposite the grinding surface (figs. 18, 20, mo.), 
is a characteristic prominent shoulder (fig. 18, hu.\ and the conical 
process (for attachment of a rotatory muscle) on the dorsal aspect 
of the base of the mandible (fig. 20, pro.) is also prominent. 
* Recorded by Wahlgren from South Shetland, Graham Land, Paulet 
Island, and South Georgia. 
t Cryptopygus cinctus, newly described by Wahlgren (1906) from Tierra del 
Fuego and East Falkland, has, like C. crassus , only twelve ocelli, and no clubbed 
hairs on the feet. It is, however, variegated in coloration when adult. 
