146 JOUKNAL OF ENTOMOLOGY AND ZOOLOGY 



head. In most species there are sixteen ocelli present. The 

 postantennal organ is usually present and is of importance in 

 species determination. The claws are two and often bear teeth 

 on inner and outer margins. The furcula may be poorly 

 developed or well developed and the mucrones are more highly 

 developed in this genus than in any of the others. 



Key to the Genu.s Isotoma 



A. Furcula short, not reaching ventral tube. 

 B. Mucrones bidenticulate. 



C. Claws unarmed ; manubrium longer than dentes ; 

 antennae little longer than the head; gray-blue 

 or brown. bidenticula 



CC. Superior claw armed; dentes twice the length 

 of the manubrium; antennae same length as 

 head ; light green in color. aquis n. sp. 



BB. Mucrones tridenticulate. 



C. Mucrones with second and third teeth opposite. 

 D. Claws unarmed. besselsii 



DD. Claws armed; superior, two teeth on 

 inner margin, two on outer; inferior, one 

 tooth on inner margin. aspera n. sp. 



CC. Mucrones with second and third tooth not oppo- 

 site, third tooth smaller; claws unarmed. 



minima 

 AA. Furcula reaching nearly or quite to the ventral tube. 



B. Mucrones, tridenticulate ; no regular markings ; inner 

 margin of superior claw bidentate ; postantennal 

 organ ovate to oval. viridis 



BB. Mucrones quadridenticulate. 



C. Long pre-apical tooth, minute apical tooth; 

 claws armed ; length 3 mm. catena 



CC. Apical tooth of mucrones projecting as far as 

 pre-apical. Dorsal median dark stripe. 



palustris 



