41U BULLETIN" 54, UNITED STATES NATIONAL MUSEUM. 



The Asellidas are mostly fresh -water forms. All the members of 

 the genera, Asellus, Mancasellus, and Csecidotea, are found in fresh- 

 water streams, wells, pools, and lakes. 

 The species Janirella Bonnier is, however, 

 marine. 



ANALYTICAL KEY TO THE GENERA OF THE FAMILY 

 ASELLID.E. 



a. Mandibles without a palp. Last six pairs of legs 

 with dactylus bi-unguiculate. 



Genus Mancasellus Harger 

 a'. Mandible with a three-jointed palp. 

 b. Eyes present. Body oblong, depressed. Head 

 small, narrower and shorter than first tho- 

 racic segment. Caudal segment not longer 



than broad Genus Asellus Geoff roy 



b'. Eyes wan ting. Body elongate, narrow. Head 

 large, not narrower than first thoracic seg- 

 ment, and longer. Caudal segment much 

 longer than broad. 



Genus Cseddotea Packard 



67. Genus MANCASELLUS Harger. 



Eyes present. 



Mandibles without a palp. Last six pairs 

 of legs with dact} T lus bi-unguiculate. Body 

 broad, depressed. Terminal segment of 

 body broad. 



ANALYTICAL KEY TO THE SPECIES OF THE GENUS 

 MANCASELLUS. 



a. Lateral margins of head entire. 



Mancasellus brachyurus Harger 

 a' . Lateral margins of head not entire. 

 b. Uropoda shorter than terminal segment of 



body. 



c. Uropoda half as long as terminal segment of 

 body. Propodus of first pair of legs armed 

 with two triangular processes. Lateral 

 margins of head with a deep cleft on either side. 



Mancasellus macrourus Garman 



c' . Uropoda two-thirds as long as terminal segment of body. Propodus of first 

 pair of legs armed with one triangular process or three acute teeth. Lateral 

 margins of head with a large rounded sinus on either side. 

 d. Propodus of first pair of legs armed with one triangular process. Sides of 



sinus on lateral margins of head not meeting Mancasellus tenax (Smith ) 



d'. Propodus of first pair of legs armed with three acute teeth. Sides of sinus on 

 lateral margins of head sometimes meeting. Mancasellus tenax dilata Harger 

 . Uropoda as long as terminal segment of body. 



c. Propodus of first pair of legs armed with one triangular process. Second pair 

 of antenme as long as or longer than the body. Inner branch of uropoda 

 nearly three times as long as outer branch Mancasellus lineatus (Say) 



FIG. 459. MANCASELLUS BRACHYUBUS 

 (AFTER GARMAN). a, MANDIBLE, b, 

 OUTLINE OF ONE SIDE OF HEAD, c, 



ONE OF SECOND GENITAL PLATES OF 



MALE, d, UROPOD. e, HAND. 



