830 PROCEEDINGS OF THE NATIONAL MUSFAJM. vol.xxiii. 



This remarkable fossil, represented by a number of specimens in 

 the U. S. National Museum {Reg. No. 147592), weighs, without any 

 extraneous matter, T pounds, and the measurements are: height, 230 

 mm. ; length 235 mm. ; diameter, 67 mm. 



The largest species hitherto recorded is the Lueina {Pseudmniltha) 

 giganied Deshayes, from the Parisian Eocene, and that hardl^^ exceeds 

 80 mm. in its maximum height. 



If we except the Tridacnacea and a few Mytilacea, Phcicoides mega- 

 meris is one of the largest pelecjq^ods known. 



Suppl&mentary note. — Some curious ab5^ssal Pelecypods from the 

 south Atlantic and the Philippines were described by E. A. Smith, in 

 the Challenger Report, under the names of Cryiytodon moseleyi and 

 C. luzonicus. The valves are almost perfectly plain and the hinge 

 edentulous. According to Pelseneer, the anatomy presents the fol- 

 lowing features: There is a single anal orifice, without valvular or 

 siphonal prolongation; the foot is hatchet-shaped, compressed, tuid 

 short, with a conspicuous byssal sulcus; the form and arrangement of 

 the adductors recalls Leptoii rather than Luc'nui or Thyasiraj the gills 

 have on each side a single direct and reflected lamina, as in Imcma,' the 

 hepatic and visceral glands are contained within the mass of the body; 

 the anal and peripedal chambers are separated by the union of the 

 gills posteriorly; the anterior edges of the mantle are thickened and 

 specialized for some — not evident — fimction; the palps are much as in 

 Dlplodonta. 



These two species are obviously not referable to Thyasira^ and the 

 simplicity of the shell, which recalls Axmulus^ gives no clue even to 

 the family to which they should be referred. On the anatomical evi- 

 dence, I propose for them the generic name of Vatlcinarla. 



From Tliyasira and its near allies, ^^atictnariii difl^ers by its lut'inoid 

 gills and the absence of hepatic digitations, as well as b^^ the special- 

 ization of the anterior mantle margin. 



From the Diplodontid(v (otherwise Ungidin'tdtp) it differs by its 

 lucinoid gills, single siphonal orilice, flattened foot, and edentulous 

 hinge. There is no evidence of any relations with the Corbida' or 

 CyrefielUdce. By this elimination we are obliged to refer the genus 

 to the Lucinida\ of which it is perhaps a degenerate member. It may 

 have lost (as many forms have) much of its character b}^ long residence 

 in the abyssal region. It is least unlikt^ such a group as Jagonia, and 

 at any rate can not I)e referred witli propriety to either the Thytmrldce 

 or DljplodontidcB. 



