90 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
Cillery thin and end in a double claw. The genital opercnluin is 
on the seventh segment, and on the eighth the appendages 
have been modified into a pair of organs corresponding to 
those wliich in later scorpions have a toothed edge andean*, 
known as pectines (combs). It is possible that the breathing 
organs on segments nine to twelve remained as in the 
b 
a 
Fig, 43. — Silurian primitive Scorpions, Palmophonus. a, P. mintiic^, 
Ludlovian of Gotland, upper surface. ^ nat. size. (R. I. Pocock, after 
Thorell & Lindstrom.) b, P. calcdonicus [Hunteri], Ludlovian of 
Lanarksliire, under surface, about twice nat. size. (R. I. Pocock.) 
(Both blocks lent by Messrs. Constable, from Lankester’s “ Extinct 
Animals.”) 
Eniypterida. But in many scorpions of Carboniferous age an 
important change has taken place in that the covering plates 
liave closed over the lamellae of tlie gills, leaving only slit- 
like openings called stigmata. Thus when the animal 
emerged from the water the lamellae remained moist, and 
breathing took place by tlie admission of air to them through 
Table-case the stigmata. They are no longer gills, but lungs. Specimens 
■Wall-case England, and a fine scorpion from Bohemia called 
13c. 
