5. Outer division of third uropods (last of three pairs of tail appendages 

 lateral to the telson) with two segments; blind; in caves of Tenn. 

 Isliphargus Hay 

 Outer division of third uropods with one segment; blind or not; more 

 generally distributed 



Eucrangonyx Stebbing 



GENERAL REFERENCES 



Holmes, S. J. 1903. Synopses of North American Invertebrates — -The Am' 

 phipoda. Amer. Nat., Vol. 37. 



Ortmann, A. E. 1918. Higher Crustaceans (Malacostraca) . Chap. 25 in 

 Ward and Whipple's 'Tresh-water Biology". John Wiley & Sons. New 

 York. 



Weckel, A. L. 1907. The Fresh- water Amphipoda of North America. Proc. 

 U. S. Nat. Museum, Vol. 32. 



KEY TO THE COMMON GENERA OF ISOPODS, SOWBUGS 



OR PILLBUGS 



1. Both pairs of antennae undeveloped; parasitic on gills of Crustacea; 



Family Bopyridae 



Prohopyrus Giard & Bonnier 

 With one or two pairs of developed antennae; not parasitic 2. 



2. Both pairs of antennae apparent (more than three-jointed) ; water forms 



3. 



First pair of antennae obscure (not more than three-jointed) ; usually 



but not always land forms 7. 



3. Uropods lateral; Family Sphaeromidae 4. 

 Uropods terminal; Family Asellidae 5. 



4. Outer side of outer branch of uropod serrate 



Sphaeroma Latreille 

 Outer side of outer branch of uropod smooth 

 Exosphaeroma Stebbing 



5. Head as wide as and longer than iirst segment of thorax; no eyes; in caves 



and wells 



Caecidotea Packard 

 Head narrower or shorter; with eyes 6. 



6. Legs (except first pair) with one claw 



Asellus Geoifroy St.-Hillaire 

 Legs (except first pair) with two claws 

 Mancasellus Harger 



7. Uropods modified to form a flattened opercular covering for the ventral 



rear of abdomen; Family Tyhdae 

 Tylos Latreille 

 Uropods each with two branches projecting backwards 8. 



189 



