No. 407.] A SINGULAR ARACHNID. 841 
movable, so as to allow the mouth to open and close. The 
muscles, which, by the bye, we have not examined more closely, 
are very strong." 
The thorax, which is quite distinct from the head, consists 
of two separate segments, each bearing a pair of limbs. In 
this respect Koenenia resembles the Tartarides and Solifuge, 
the only other arachnids with a bisegmental thorax. 
The six pairs of limbs are, with the exception of the first 
pair, or chelicerz, of a remarkably simple structure. Even the 
chelicerze are of a primitive type, in that they consist of three 
joints. They are said by Hansen and Sórensen to * correspond 
entirely with the type appearing in the Opiliones," except in 
their minuter characters. The insertions of their long and 
powerful first joints are slightly to the sides of the mouth ; 
a very significant fact, since in all the higher Arachnida these 
organs are definitely preoral. The second and third joints 
of each chelicera form a pair of pinchers. Each of these 
joints is furnished with a dense series of eight slender, 
pointed teeth. i 
The second to sixth pairs of appendages have essentially the 
same simple type of structure, although the pairs differ in 
length and in the number of joints. The formula of their 
lengths is as follows : 
45>65>2>5> 4. 
The second pair have nine joints, the third twelve, the fourth 
and fifth each seven, the sixth eight joints. All the legs ter- 
minate in two claws and a curved pseudonychium. All are 
provided with a coxa, trochanter, and femur. The third to 
sixth pairs have a separate patella and tibia, but these two 
joints are represented by a single piece in the second pair. 
“The metatarsus is two-jointed in the second pair of limbs, 
four-jointed in the third pair, and undivided in the fourth, fifth, 
and sixth pairs.” The “tarsus is three-jointed in the second 
and third pairs of limbs, one-jointed in the fourth and fifth, two- 
jointed in the sixth." ! 
Although the second to sixth pairs of limbs are all used in 
1 Hansen and Sörensen, /oc. cit., p. 230. 
