REVISION OF RECENT BAIRDIIDAE 17 



rows plus posterior inserted wedge; distal antennal claw of male with 

 sigmoid incision, anterodistal seta thin, fused claw smooth; first 

 thoracic leg with 4 unfeathered setae of vibratory plate widely spaced; 

 furca ^nth 7 setae, the last two very tiny; male copulatory organ of 

 simple hinged 3-part structure ^nth stiff arched copulatory tube. 



Description. — Carapace thin, smooth or faintly pitted; lateral 

 outline var3dng from ovate to subrhomboidal, lacking any posterodor- 

 sal concavity or pronounced ventral sinuation, posterior end usually 

 acutely tapered; anterior margin of right valve with or Avithout few 

 short denticles, left anterior margin smooth, left or both posterior 

 margins edged with fine denticles; posteriormost spine may be en- 

 larged to long spine or platelet supporting posterodorsal siphonate 

 projection formed by fused lamelUform setae. Eight elongate adductor 

 muscle scars arranged in three horizontal-diagonal rows and a fourth 

 wedge-shaped inserted row. Epidermis deeply pigmented in whole or 

 part, accounting for dark brown color pattern of living animal; medial 

 oval opaque pattern, rarely any other pattern. Hinge thin and simple, 

 median elements may be very finely striate. Fused marginal zone 

 moderately wide, radial pore canals straight and abundant. 



Antenna with fifth podomere very long and thin, more than twice as 

 long as fourth; sixth podomere fused with stout simple curved claw, 

 smooth in both sexes, carrying besides the distal claw an anterodistal 

 seta and an extremely thin rodlike sensory (?) seta; distal claw very 

 long and sturdy, in males cleft by a sigmoid incision into a bifid hook, 

 in females tapering smoothly to a slender point; anterodistal seta 

 short and thin or absent in males, long but thin in females, extending 

 to two-thirds the length of distal claw. Vibratory plate of first thoracic 

 leg wath four unfeathered, more heavily chitinized setae spaced 

 widely along the ventral margin; male mth the first two of these 

 setae closely grouped at anteroventral corner and directed ventrally, 

 others directed posteriorly; female with only the first seta so segre- 

 gated. AU thoracic legs with podomere 4 long and slender, more than 

 twice as long as podomere 3, distal claw long and thin and tapering to 

 simple point. Furca generally with 7 setae, seta 2 twice as long as 

 others and feathered, setae 6 and 7 very much shorter than others. 

 Male copulatory organ of relatively simple, hinged 3-part structure, 

 with the three lobes distinctly separable, terminal lobe very much 

 smaller than median lobe and with digitate protrusions very small or 

 absent; copulatory tube reaches in a broad stiff arch from junction of 

 basal and median lobes to beyond tip of median lobe, there generally 

 penetrating and emerging distally beside terminal lobe as slender 

 flexible thread. 



