1046 JOURNAL, BOMB AY NATURAL HIST. SOCIETY, Vol.XXYIlI. 
The sound-producing organs of these spiders consist of specialised teeth or 
spines on the opposed surfaces of the basal joints of the chelicerae and palps, 
but they are not present in all genera. They were first discovered in 
ChilohracJiys (‘Mygale’) stridulans, which is said to make a noise that “ is 
both peculiar and loud ; it resembles that made by pouring out small shot 
on to a plate from a height of a few inches, or, better still, by drawing 
the back of a knife along the edge of a strong comb While stridulating 
“ the spider usually rested on the four posterior legs, raising the other 
four and shaking them in the air, -with the thorax thrown up almost 
at right angles to the abdomen and the chelicerae in rapid motion — 
assumed in fact, quite a threatening attitude” (Trans Ent. Soc. London, 1877, 
pp. 281-2, pi. VII; pi. reproduced as fig. 1 of present paper). It is 
interesting to note that the sound produced by C. stridulans is much louder 
than that made by C. fiimosus, as the stridulating organs of the former are of 
more highly specialised structure than are those of the latter. 
The Trapdoor-spiders belong to two distinct subfamihes, the Ctenizinae 
and the Barychdinae, but not aU species of these subfamilies close the mouths 
of their abodes with trapdoors. So far as my observations go, the abodes of 
the Ctenizidae are more or less elongated burrows with a single opening each, 
whereas those of the Barychdinae are shorter and broader with two apertures 
(see fig. 2). The burrows of some of the Ctenizidae ( e.g., Nemesiellus 
montanus) are, however, forked near the bottom with an internal trapdoor at 
the fork which can be pulled across so as to shut off whichever branch the 
spider choses to hide in (fig. 2o). The trapdoors may be thin and “ wafer ” 
like falUng over the aperture they have to hide ; or they may be stout and ' 
“ cork ” like, fitting tightly into the aperture. In either case they are difficult 
to detect, being composed of silk covered on the outer surface with soil, etc.;' 
but whereas in the former case there is only one layer of silk, in the latter a 
number of layers are imited one on top of another. 
Males have to leave their nests in search of mates, but ■with this 
exception these spiders probably never go out except through misadventure, 
resting on the irmer side of the trapdoor till a fly aUghts on the outer side, when' 
the door opens and the fly disappears with Hghtning rapidity. If a specimen 
is removed from its nest it appears to have no knowledge as to how to make a 
new one unless it is pro-vided with some sort of burrow to start -with, 
in which case this will be provided with a trapdoor, enlarged if necessary, 
and fined ■with silk. Otherwise the spider wanders about rmtil after a day or 
two it dies, ■without attempting to make a new burrow for itself. 
Further observations on the habits and nests of various species of Trapdoor- 
spider are much to be desired. All the species so far described have been My- 
galomorphs belonging to one or other of the two above mentioned subfamilies ; 
but in Madras there is a species belonging apparently to the Arachnomorph 
family Zodaiiidae which like'wise closes the entrances to its nest ■with trapdoors. 
The Araneae Verae or Arachnomorphae can be di'vided into two groups, 
the Crihellatae and Ecribellatae, according to whether a cribeUum or spinning 
plate IS present or not in front of the spinerettes ; and this classification is 
commonly adopted, though it is by no means certain that it is a natural one, 
since certain Cribellate families appear in other respects to be more closely re- 
lated to different Ecribellate families than to each other. 
Stegodyphus sarasinorum (Fam. Eresidae), a common social spider ■widely 
distributed throughout India, is among the most interesting of the Crihellatae. 
It spins dense untidy cobwebs among the branches of trees and bushes, each of 
these being as a rule the home of a large number of spiders (fig. 3). From 
these nests sheets of very sticky and elastic silk extend outwards, and woe 
betide any insect unwary enough to fall into one of them. For immediately the 
spiders find that anything has been caught they swarm out and together drag if 
