842 THE AMERICAN NATURALIST. |. [Vor. XXXIV. 
running, the very long third pair are usually held aloft like 
antennz when the animal is not disturbed and is moving 
about slowly. Some of the metatarsal and tarsal joints of 
this pair of appendages are provided with very long, delicate 
hairs of uniform thickness throughout. They are very prob- 
ably sense-hairs (possibly auditory in function, as suggested 
by Hansen and Sörensen). 
Between the insertions of the legs the ventral surface of the 
head and thorax presents a series of sternal plates to which the 
Danish arachnologists have called particular attention. The 
lower surface of the head has two of these plates, a larger 
anterior one just behind the mouth and corresponding to the 
second and third pairs of appendages, and a smaller piece cor- 
responding to the third pair of limbs. Farther back there are 
two more sternal plates, one to each of the thoracic segments. 
The condition of the sternal apparatus of the head is empha- 
sized “as a curiosity, as it is quite unique in Arachnida, which 
otherwise show no trace of independence in the segments con- 
stituting the head.” ! 
The abdomen is elongate elliptical in outline, without any 
traces of dorso-ventral flattening, and consists of eleven seg- 
ments. The first is short and narrow, and on this account may 
be readily overlooked. The ninth, tenth, and eleventh are very 
much narrower than the preceding segments. The last bears 
the anus on its ventral surface. To its posterior surface the 
caudal flagellum is attached. The dorsal surfaces of the ab- 
dominal segments each presents a single row of bristles which 
are inserted rather far apart and near the middle of their 
respective segments. 
Hansen and Sórensen have failed to give a satisfactory 
account of the ventral surface of the abdomen. The condi- 
tions are not so easily studied as might at first sight be sup- 
posed. Nor am I certain that my analysis of this region is 
complete, as my specimens differ considerably in the clearness 
with which they show certain structures, notably the com- 
plicated valves surrounding the genital orifice. I am of the 
opinion that segments two to six are each provided with a 
1 Hansen and Sörensen, /oc. cit., p. 226. 
