REVISION OF RECENT BAIRDIIDAE 55 



Type specimens.^ — Holotype specimen USNM 121309; paratypes 

 USNM 121310-121314. 



Type locality. — Albatross station 2751. 



Diagnosis. — Surface smooth mth \\ddely spaced tiny normal pore 

 canal pits. Left valve rounded subtriangular in lateral ^aew, right 

 valve more nearly trapezoidal. Well preserved specimens have tiny 

 marginal denticles on both valves, most specimens are more or less 

 abraded Mith smooth margins. Typical form mth dorsal rows of 

 adductor muscle-scar pattern divided into 3 scars each and separated 

 by a gap; ventral scars also tend toward further subdivision. 



Material.— One female Uving at USNM, Ace. No. 271766; 319 

 subfossil specimens at Albatross stations 2385, 2392, 2751, 2808, 3376, 

 and at Anton Bruun stations 360B, 363G,J,K, 367D, 368C, 369G, 

 J, 397D, 400B, 407. 



Dimensions. — Left valve specimen USNM 121310, length 1.39 mm, 

 height 0.98 mm. 



Right valve specimen USNM 121311, length 1.48 mm, height 

 0.98 mm. 



Left valve specimen USNM 121309, length 1.40 mm, height 

 0.90 mm. 



Right valve specimen USNM 121312, length 1.40 mm, height 

 0.87 mm. 



Affinities. — While it may seem improbable that so widespread a 

 form should not have been described previously, I cannot find any 

 illustrated species with which to identify it. I suspect that specimens 

 of this form might have been recorded as Bairdia victrix Brady by 

 Brady (1880), Chapman (1910), and Tressler (1954), but cannot 

 prove this. 



Bairdia subcircinata Brady and Norman, described from the North 

 Atlantic and (as B. jormosa Brady) from various Challenger dredgings, 

 is relatively higher in lateral view and has tiny spinose tubercles on 

 the lateral surface. 



Bairdia subdeltoidea conjormis Terquem of Colalongo (1965), 

 described from the Plio-Pleistocene of Calabria, has smooth margins 

 on both valves and a more upturned posterior angle in left valve, also 

 apparently has denticulate hingement. 



Mozambique Channel specimens are generally higher in proportion 

 to length and display a conspicuously different muscle-scar arrange- 

 ment (Figure 28/, m) ; however, there exists such a diversity of form in 

 this population that some specimens cannot be distinguished reliably 

 from the western population. For the time being, the populations from 

 the Gulf of Mexico, Pacific, and Mozambique Channel are identified 

 with the Caribbean species. 



