REVISION OF RECENT BAIRDIIDAE 67 



anterodorsal segment and concave posterodorsal segment; right valve 

 with obscurely angulate tripartite dorsal margin, anterodorsal and 

 posterodorsal segments straight or slightly concave, posterior dis- 

 tinctly caudate, ventral margin slightly indented. Curvature of lateral 

 surface very gentle, without any abrupt changes in slope, moderately 

 expanded medially, more compressed marginally and ventrally. 

 Hinge-proper simple and usually quite thin, median bar of right valve 

 of equal thickness throughout; auxiliary dentition present at antero- 

 dorsal and posterodorsal angles at location of greatest marginal con- 

 cavity, consisting in right valve of 4-6 tiny denticles surmounting 

 anterodorsal or posterodorsal marginal ridge, in left valve of visibly 

 locellate or crenulate arcuate grooves with ventral confining rise, 

 located directly underneath overhang of dorsal surface. Muscle-scar 

 pattern consists of 8 subcircular to subquadrate scars arranged in 

 three horizontal to arcuate well separated rows, scars of dorsal or 

 ventral rows tending to be divided for a total of 10 scars. 



Antenna of both sexes with near-duplicate, pincer-form, immovable 

 terminal claws, caused by the enlargement of the anterodistal seta of 

 the sixth podomere to equal or nearly equal the distal claw in size 

 and shape; all claws smooth and simply tapering, slightly curved, 

 none barbed or serrate. Vibratory plate of first thoracic leg with 4 

 unfeathered setae of equal length segregated proximally. Furca with 

 7 setae, of varying lengths but all fairly long, none vestigial. Copula- 

 tory organ with massive hemicircular median lobe, bulbous distal 

 lobe, long spirally coiled copulatory tube without conspicuous lamellar 

 supporting structure, may have additional projecting structures. 



Species included. — Recent species for which soft parts have been 

 described, listed by original binomen: 



Bairdoppilata alcyonicola, new species 

 Bairdop-pUata cratericola, new species 

 Nesidea cushmani Tressler, 1949 [—Bairdoppilata carinata Kornicker, 1961; 



= Bairdoppilata triangulata Edwards of Benson and Coleman, 1964] 

 Bairdia hirsuta Brady, 1880 

 Bairdia simplex Brady, 1880 

 Bairdia villosa Brady, 1880 



Ecology. — Recent species of Bairdoppilata (Bairdoppilata) are 

 abundant in tropical and subtropical regions in very shallow-water 

 niches as epifauna on coralline and rocky reefs, algae, sea grasses, 

 corals, sponges, other attached invertebrates, and associated skeletal 

 debris. The three Challenger species assigned below to this group from 

 abyssal depths and/or much colder water also share several discordant 

 features of carapace and genital anatomy; they should certainly be 

 allocated a new subgenus within Bairdoppilata when more plentiful 

 living material becomes available. 



