Fossil Scovpions 129 



Family Cyclophtlialmidae 



Genus Eoctonus Petrunkevitch (1 species, American). 

 Family Eoscorpionidue. 



Normal arrangement of coxae, pentagonal sternum. 



Genus Eoscorpiua Meek and Wci'then, 1868, (8 species, 4 Ameri- 

 can and 4 European). 



Genus Trigonoscorpio (1 species, American). 



Genus Palaeopisthacanthus (2 species, American). 



Genus Microlabis Corda, 1839 (1 species, European). 

 Family Mazonidae. 



Middle eyes close to anterior edge of cephalothorax. Structure 

 of pedipalpi and sternum unknown. 



Genus Mazonia Meek and Wcrthen, 1868 (1 species, American). 



The classification proposed by Petrunkevitch has the advantage that 

 it is based on characters ascertainable even from fossil specimens, al- 

 though derived from the comparative anatomy of recent forms. This 

 classification will be followed as closely as possible in the description 

 of the specimen in hand. 



Comparison of Fossil Scorpions to Modern Fotdis. In the compari- 

 son of most fossil organisms with living forms usually only the broader 

 features can be considered, for the finer generic and specific characters 

 upon which modern forms are differentiated are commonly lacking to 

 a greater or less degree. This condition is met with among the Pale- 

 ozoic scorpions. The general morphology of scorpions has changed but 

 little since Silurian times, the greatest modifications being in the struc- 

 true of the legs and feet and the much debated breathing apparatus. 

 It has been suggested by some authors, after a comparison of the shape 

 of the bodies of some fossil scorpions, that the viviparous habit was 

 acquired before Carboniferous times. These characters may have fol- 

 lowed as a result of the change from an aquatic to a terrestrial habitat. 



Brief Notes on the Morphology of Modern Forms. — Only the ex- 

 ternal characters with which this paper is concerned, will be considered 

 here. 



Scorpions are animals with a segmented chitinous exterior skeleton, 

 the anterior segments of vi^hich are fused to form the cephalothorax. 

 The praeabdomen is composed of seven broad, thick, movable segments 

 which surround the principal viscera. A prolonged extension of the 

 praeabdomen, consisting of five segments, is known as the postabdomen. 

 The last segment of the postabdomen is armed with a stout curved spine 

 which bears at its extremity the opening of two ducts leading from a 

 pair of glands lying in the twelfth abdominal segment and secreting a 

 poisonous fluid. 



The first pair of appendages are called the chilicirae and are sit- 

 uated in front of the mouth. These appendages are chelate. The next 

 pair of appendages are the strongest appendages and are provided with 

 chelae. Their chief service is in grasping and bringing food to the 

 mouth. The coxae of the second, third and fourth pairs of appendages 

 are situated about the mouth and serve as jaws. Behind the pedipalps 



9—25870 



