President's Address. 375 



the large clielicerse, and the fact that the walking limbs are 

 tipped with only a single claw. 



In 1889, while working out the collection of Merostomata 

 from the Wenlock rocks of the Gutterford Burn in the 

 Museum of Science and Art, Malcolm Laurie discovered the 

 remains of a Scorpion, which he described under the name 

 of Palceophomis loudonensis} This species, from a lower 

 horizon than any other yet discovered, agrees in most 

 respects with the characters of all the other Silurian forms ; 

 but Professor Laurie observed indications of curious plate- 

 like appendages on the ventral surfaces of the mesosomatic 

 segments, suggesting that either they were gills or that " gill- 

 bearing appendages had not become completely fused with the 

 abdomen to form an air-chamber, as in recent forms." ^ 



With regard to the Carboniferous Scorpions, that which 

 strikes the observer is their extreme likeness to modern 

 ones, the chief difference being in the larger size and more 

 forward position of the central eyes, and also the relatively 

 longer size of the pentagonal sternal plate in the older forms. 

 Indeed, there seems to be greater differences among some 

 recent species themselves than there is between some modern 

 Scorpions and the Carboniferous ones. This is, perhaps, not 

 so very astonishing when we consider that the Scorpions 

 are the most generalised and most archaic form of living 

 Arachnids. 



MYEIAPODA. 



Up to the time when I brought before our Society a paper 

 on Kampecaris and Archidesmus, from the Lower Old Eed 

 Sandstone of Forfarshire, and which is published in our 

 Proceedings for 1882, the oldest known Myriapods were from 

 the Carboniferous formation,^ — two species of Chilognathous 

 Myriapod, which differ from all recent and known fossil 

 forms in having the tergal and sternal elements of each 

 segment free from those of neighbouring segments, so that 

 each body-ring bore only a single pair of limbs. For one 



1 Trans. Roy. Soc. Edin., vol. xxxix. p. 375, 1899. 



2 Mem. Geol. Sur., "The Sil. Rocks of Britain," p. 598. 



■^ Proc. Roy. Phys. Soc. Edin., vol. vii. pp. 177, 178, 1882. 



