THE TARANTULAS 117 



clay surfaces are partially covered with mosses and liverworts. The 

 burrows are straight, cylindrical, and almost vertical in every in- 

 stance. They are enlarged for two-thirds their upper length, then 

 narrow abrupty until they are exactly the diameter of the hard 

 abdominal disk of the occupant. Specimens are usually found head- 

 first in the bottoms of the burrows, presenting their armor plate 

 to the intruder. In this position they fit the cylindrical cavity so 

 nicely, and they hold on with their claws so tenaciously, that it is 

 necessary to dig the earth away in order to extricate them without 

 injury. When disturbed, some back up their burrows to where 

 there is room for them to turn and present their fangs. 



The burrow of Cyclocosmia is covered by a hinged trap door, 

 which is similar in shape to that of Pachylomerus but much thinner 

 and quite flexible, thus belonging to the wafer type. Most of the 

 doors appear to be located in and under leafmold on the sides of 

 the banks, a circumstance that makes them difficult to locate. 



It has now been established that Cyclocosmia is simply another 

 trap-door spider, but an extraordinary one; what, therefore, can 

 we conclude regarding the previous interpretations by older stu- 

 dents of the use of its abdomen, interpretations that have persisted 

 even into recent books and papers? Obviously, it is disproved that 

 the spider closes the top of the burrow with its abdomen. In addi- 

 tion to the fact that there is a wafer trap door covering the en- 

 trance, it is impossible for the abdomen to plug the outer opening, 

 because of the difference in diameter. Cyclocosmia seemingly has 

 two lines of defense against enemies: its well-hidden surface door 

 and its ability to run down to the bottom of its burrow and com- 

 pletely plug the tube. (See Text Fig. 3, C.) 



The protective devices of the trap-door spiders herein considered 

 may be briefly reviewed as follows: Pachylomerus and Bothriocyr- 

 tum rely upon a fortress guarded by a heavy cork door, which they 

 hold shut with surprising strength. Myrmekiaphila and Actinoxia 

 build a weak, flexible cover that serves only to keep out rain, but 

 is well camouflaged; they depend upon the deception of the con- 

 cealed side chamber deep within their burrow. Cyclocosmia trun- 

 cata carefully hides the wafer door to its nest, and to intruders 

 presents its tough body armor as a shield. 



Sheet-Web Tarantulas. The spiders of the family Dipluridae 

 have followed a course in their development quite different from 

 either the trap-door spiders or the tarantulas. They spin a silken 



