306 E. I. POCOCK. 



the uninterrupted outline presented by the somites in question, 

 which imparts so natural an appearance to this region, is thus 

 the result of pure accident I find hardly credible. In fact, 

 there is, I think, no reason to doubt that the fifth and sixth 

 mesosomatic somites were united to the metasoma, and shared 

 its unmistakable inversion. Hence the plates in question are 

 sternites. The important point attached to this conclusion 

 is the absence of stigmata on these sternites. Perhaps it was 

 this fact which led Thorell to his decision as to their tergal 

 character. 



The above-given reasons justify a sceptical attitude towards 

 the alleged existence of stigmata in the Gotland Palseopho- 

 nus, at all events until a further examination of the specimen 

 settles the points now under dispute. And since I found no 

 distinct traces of stigmata in the Scotch specimen, I am in- 

 clined to believe that Peach fell into error on this point 

 perhaps influenced in part by the alleged presence of stigmata 

 in the Gotland example, perhaps in part by the assumption 

 that a form so closely resembling recent scorpions in other 

 structural details must also resemble them in the nature of 

 its respiratory organs. 



To the belief in the presence of stigmata, implying the 

 existence of organs fitted for aerial respiration, coupled with 

 the knowledge of the terrestrial habits of all living scorpions, 

 is traceable the conviction evinced by jnost previous writers 

 that these Silurian scorpions lived on the land. This belief 

 is less easy to reconcile with the facts that both the known 

 specimens are relatively in an admirable state of preservation, 

 and were met with in strata of undoubted marine origin, 

 containing abundance of admittedly marine organisms, than 

 the belief, which I hold, that Palseophonus lived in the sea, 

 probably in shallow water, its strong, sharply pointed legs 

 being admirably fitted, like those of a crab, for maintaining 

 a secure hold amongst the seaweed or on the jagged surface 

 of rocks, and for resisting the force of the rising and falling- 

 waves. 



Respiration, as already suggested, may have been effected 



