356 PROCEEBINGSi OF THE NATIONAL MTIREVM. vol. xxvi. 



Section Artena Conrad, 187<). Type, Venus staminea Conrad. 

 Miocene. 



Shell trigonal or short, with acute concentric laminae, between which 

 are minute elevated concentric lines; lunule not deep; escutcheon 

 large, not overlapping; posterior right cardinal narrow, laminar; other 

 features as in Antigona. 



This section bears to Antigona much such a i-elation as Ventricola 

 does to typical Cytherea., in the other subgenus. It was called Artenia 

 by Try on in 1884. 



Subgenus Circomphalus Morch, 1853. Type, Vhiiis plicata Gmelin 

 (= Y. dysera Liniueus j;/'c>/M/'/'t^). 



Shell cordate, compressed, with distant elevated reflected laminae 

 which have leaflike expansions near the posterior border; lunule and 

 escutcheon, impressed, striate, sharply limited, unequally divided 

 between the valves; ligament deeply sunken; inner margins crenate, 

 pallial sinus small, triangular; anterior right and posterior left cardi- 

 nals slender, laminar, entire, the others bifid; a minute pustular ante- 

 rior left lateral present. 



This is Analtis Tryon, 188-1, not of Duponchel, 1829, or Romer, 18.57; 

 and Ohiona Romer, 1857, not of Morch, 1853. V. calophylJa Hanley, 

 also belongs here. 



Subgenus Lepidocardia Dall, 1902. Type, CMone fiorkleUa Gray 

 (+ Vemis africana Philippi). 



Shell small, compressed, donaciform, smooth or concentrically 

 striated, polished; lunule defined, but there is no defined escutcheon; 

 internal margins smooth; pallial sinus linguiform, pointed in front, 

 horizontally directed, partly confluent with the pallial line below; 

 dorsal margins beyond the hinge plate grooved; teeth delicate, the 

 anterior laterals well developed, the posterior right and anterior two 

 left cardinals more or less distinctly grooved. 



Though compressed, this form recalls Gompliina by its external 

 characters. 



Genus SAXIDOMUS Conrad, 1837 



Type, S. nuttalUi Conrad. 



Shell large, rude, chalky, ovate-quadrate, with low beaks, and con- 

 centric usually feeble sculpture; the ligament is strong and not 

 depressed; there is no defined lunular area or escutcheon; internal 

 margins smooth; pallial line with a deep, rounded siiuis; hinge with 

 three cardinals in each valve; the posterior right cardinal bifid; anterior 

 laterals closely adjacent to the cardinals, one of the left ones often in 

 line with the anterior cardinal. 



Shores of the North Pacific. 



This group has been generally misunderstood and placed, as by 

 Deshayes, near Tapes. His group of radial sulcate Saxidormis, of 1853, 



