KESPlliATOKY OKGANS IN AHANEiE. 
48 
(Drassodes tesselatus), Sicariidie (Scytodes tes- 
tudo); also iu the following Tetrapneumonous spiders 
(Aviculariidse) : subfam. Avicu lar i inse (Harpactira 
atra)j subfam. Cteuizinae (Sbasimopus unispiiiosus 
and Her mac ha sp.). 
In the following forms the septa were inclined at an angle 
of 45° or less to the horizontal, sloping downwards from the 
higher medial edges to the lower lateral edges : Argiopidae, 
subfam. Argiopiuae (Argiope clathrata), Theridiidm 
(Latrodectus geometricus), and Eresidie (Eresus 
sp.). 
If the above examples are any indication of the usual posi- 
tion in the families to which they belong, then Horner’s state- 
ment niust be wrong, and cannot hold good for the great 
majority of Araneie. Even in the three cases where the 
septa were incliued they were nearer the horizontal than the 
vertical (except, perhaps, in Latrodectus geometricus, 
where they formed an angle of about 45°). 
Moreover, the operculum iu the spiders with horizontal 
septa is similar to that of Attus floricola described on p. 
49 (see hg. 17), and since this type of operculum represents 
that of any Dipneumonous or Tetrapneumonous spider in 
which the abdomen is not greatly developed anteriorly, we 
may faiidy assume that the septa must be horizontal, or very 
nearly so in the great majority of s})iders. 
^Vllen, however, the anterior upper region of the abdomen 
is abnormally distended above the opercula, it may happen 
that the lateral region of the latter becomes pushed down- 
wards into a more horizontal position than is the case in 
fig. 17, and at the same time the septa become tilted upwards 
on the medial side, that is to say, they take a more or less 
incliued position, such as one finds in Argiope, Latro- 
dectus, and Eresus, and no doubt in many other genera of 
the same families, d'he inclined position of the septa cannot, 
therefore, be a primitive condition in these families, but, I 
think, merely due to the abnormal distension of the abdo- 
men, for iu closely allied forms, in which the abdomen is not 
