105 (3) Pronotal hypomeron with a transverse or oblique ridge; 



body plump and convex; near streams... LIMNICHINAE ... 106 

 Hypomeron without a ridge; body more elongate; on 



ocean mudflats or beaches (Fig. 115) ... CEPHALOBYRRHINAE 



Throsoinus (species not 



included in key since they seem unrelated to water quality) 



106 (105) Antennae distinctly clubbed; pronotum with smooth 



anterolateral cavities for reception of antennae; 

 ovoid and compact; shiny reddish to black; 0.8-1 mm 

 long, 0.65-7 mm wide: Physemus minutus 



Antennae not clubbed; pronotum without cavities for 



reception of antennae; usually well over 1 mm long ... 107 



Figs 115-116 Dorsal view of adult: 115- Throsoinus schwartzi; 

 116- Linmiohus sp. 



107 (106) Small (1.2-2.3 mm long); antenna slender, with 10 



segments; first abdominal stemite with grooves for 

 reception of folded hind legs (Fig. 116) : Lirmichus 

 (Although 28 species have been described from the United 

 States, none are known to be aquatic either as larvae or 

 adults, so no attempt is made here to provide a key to 

 them.) 

 Larger (2.5-4.2 mm long); antenna with 11 segments, 

 the first two enlarged and the remaining nine sub- 

 pectinate; first abdominal sternite without grooves 

 for the reception of folded legs (Fig. 117) .Lutroahus . .108 



108 (107) Apical segment of maxillary palp subequal in width to 



apical segment of labial palp; densely pubescent with a 

 yellowish cast, but dark brown where cuticle is exposed; 

 3-4.2 mm long, 1.75-2.3 mm wide: Lutroahus arizonicus 

 Apical segment of maxillary palp not over three 



quarters as wide as that of labial palp 109 



50 



