6 ARKIV FÖR ZOOLOGI. BAND 2. N:0 8. 



Ave ha ve investigated only in this species, may show any 

 difference in other forms. 



Cephalothorax (Pl. 1., figs. 1 a — 1 d). — Dorsally (and 

 below) it is divided into an oblong head and two thoracic 

 segments. 



The head is anteriorly produced into a kind of roof above 

 the basal portion of the antennse; when it is seen from the 

 side (fig. 1 d) a movable low transverse curved plate {ji) is 

 observed under the produced anterior portion. The front 

 part of this plate is directed downwards and forwards termi- 

 nating in a less or more produced point; from this point the 

 plate projects backwards forming the lower wall of the roof 

 above the antennae, and when it is seen from the side its 

 posterior part is hidden beneath the lateral wall of the head ^ 



In Oxopoei the eyes, as well known, are distribut ed into 

 a f rontal group and two lateral ones. In Tartarides the 

 frontal eyes are always wanting. In Trithyreus Camhridgei 

 Thor. one pair of whitish lateral eyes are present, placed at 

 some distance from the lateral margin of the head above the 

 mandibles (»maxillse» auctorum); each eye has a circular. 

 vitreous cornea conspicuously more convex than the surrounding 

 chitine; that the eyes present a convexity of their own is 

 already mentioned by Thorell. Real lateral eyes are wanting 

 in all other species hitherto observed; in some species we 

 find that the corresponding place shows a light-coloured spöt, 

 a kind of eye-spot, but it is not sharply circumscribed, and 

 its surface has the same reticulated appearance as the re- 

 mainder of the head. The surface of the head is adorned 

 with a few pairs of set se. 



The first thoracic tergite (Pl. l.^ fig. 1 b, 6) is very short 

 and always divided into two small plates by a very broad 

 membrane in the middle. These plates are narrowly triangulär 

 with the very short side situated in a line with tlie lateral 

 margin of the second tergite ; from this outer margin the plate 

 stretches itself upwards and somewhat backwards towards the 

 mesial line, terminating rather distant from it in a point. 

 The second thoracic tergite (Pl. 1., fig. 1 b, c) is a rather large 

 plate, much broader than long. with the anterior margin conside- 



^ The sternum of the head and the thorncie sternites are deseribed 

 below. 



