60 Mr. J\. I. Pocock on a new 



a puzzle, and would probably have remained unsolved, so far 

 at least as I was concerned, had it not been tor Burchell's 

 until now unpublished discovery of three-quarters of a century 

 ago. Probably the absence of the granules on the depressed 

 sternal area in R. junceus, suggesting as it did the secondary 

 importance of their association with the sternal depressions 

 and with the pectinal expansions in R. Borellii, coupled with 

 the flexibility, comparative softness, and known sexual 

 physiological significance of the pectines in these and all 

 other sections, combined to conceal the true construction, 

 which, thanks to Burchell's observation, is now known to be 

 assignable to the features in question. 



How, then, is the sound described by Burchell as " between 

 a hiss and a whistle" produced ? Without doubt by sweeping 

 the pectines across the granular field on the overlying sternal 

 plate (PL IV. fig. 2). When one of these organs is turned 

 over it may be noticed that the teeth opposable to the granular 

 area are not parallel-sided, as is normally the case in scorpions; 

 the distal edge is sinuous, presenting towards the apex of the 

 tooth a very decided bulge, which shows up as a slightly 

 thickened area as it catches and reflects the light. AVhen 

 examined under a half-inch objective, or even a lower power, 

 practically the entire face of the tooth, and especially the 

 bulging area, is seen to be covered with a multitude of fine 

 stria? lying parallel to the longitudinal axis of the tooth 

 (PI. IV. fig. 3). That the structural modifications of the teeth 

 above described are directly connected with the depression and 

 granulation of the sternum is shown by the absence of such 

 modifications in the teeth at the distal end of the series which 

 lie beyond the granular area and sweep clear of it with the 

 movement of the pecten. No doubt the expansion of the 

 shaft of the pecten in its proximal half is correlated with an 

 increase in the size of its muscles and of the surfaces to 

 which they are attached to add force to the sweep of the 

 organ. 



Except for the apparent absence of the granules, the sternal 

 depressions in R. junceus closely resemble those of R. Bo- 

 rellii. I originally described these depressions as smooth ; 

 this is only true relatively speaking. No granulation is 

 visible under a lens of low power, and no roughness is per- 

 ceptible with a pin-point ; but when scrutinized with a half- 

 inch objective the entire surface of the depression is seen to 

 be exceedingly minutely shagreened, so minutely as to suggest 

 that the sound emitted must be much finer than that 

 which the organ in R. Borellii gives out. Nor is this all the 



