90 GUIDE TO THE FOSSIL INVEETEBRATE ANIMALS. 



G-allery 

 VIII. 



bearing similar appendages. The first two pairs of tliese 

 have strong pincer-claws, the next four pairs are stout and 

 end in a single claw, whereas in later scorpions they are 

 thin and end in a double claw. The genital operculum is 

 on the seventh segment, and on the eighth the appendages 

 have been modified into a pair of organs corresponding to 

 those which in later scorpions have a toothed edge and are 





\vjr/ 



0 



m 



1 



f 







b 



Fig. 43. — Silurian primitive Scorpions, Palseoplionus. a, P. nuntius, 

 Ludlovian of Gotland, upper surface, f nat. size. (E,. I. Pocock, after 

 Thorell & Lindstrom.) b, P. caledonicus [Himteri], Ludlovian of 

 Lanarkshire, under surface, about tw^ice nat. size. (E.. 1. Pocock.) 

 (Both blocks lent by Messrs. Constable, from Lankester's " Extinct 

 Animals.") 



known as pectines (combs). It is possible that the breathing 

 organs on segments nine to twelve remained as in the 

 Eurypterida. But in Eoscorpius of Carboniferous age an 

 important change has taken place in that the covering plates 

 have closed over the lamellae of the gills, leaving only slit- 

 like openings called stigmata. Thus when the animal 

 emerojed from the water the lamellae remained moist, and 



