244 PROCEEDINGS OP THE MALACOLOGICAL SOCIETY. 



triangular, generally solid, the posterior narrow and feebly grooved. 

 In the left valve the anterior is very long, the median thick and feebly 

 grooved, the posterior very thin. The left anterior and the right 

 median are sometimes feebly grooved. 



GOMPHINA, s.s. 



Type, Venus donacina, Chem. 



Shell nearly equilateral, smooth or nearly so, right nymph and left 

 posterior tooth bearing one or two ridges in donacina, and having 

 a rugose surface in G. undulosa. Pedal scar separate from that of the 

 anterior adductor. 



Species. — G. donacina, Chem., with vars. cequilatera, melancegis; 

 G. undulosa, Lam. {=V. variabilis, Sow., non Phil.). 

 LiocxMA, Dall. 



Subgenus. Type, Venus fluctuosa, Gould. 



Shell ovate-trigonal, inequilateral, concentrically grooved, with 

 a bright vernicose periostracum. Nymphs and teeth smooth. The 

 grooving of the teeth very feeble and sometimes obsolete. Pedal scar 

 not quite separated from the adductor. 



Species. — G, [Liocyma) fluctuosa, Gould {= V. astartoides, Phil.) ; 

 G. (Z.) Becki, Dall (North Japan and Alaska); G. (Z.) viridis, Dall 

 (North Japan and Alaska) ; G. (Z.) Scammoni, Dall (British Columbia), 



Genus MAKCIA, Adams, 1857, 



Generic characters. — Shell oval, oblong or subtrigonal, inequilateral, 

 smooth, or concentrically striated, Lunule defined and circumscribed, 

 escutcheon not defined, except by absence of sculpture when that is 

 present. Margins of valves smooth. Pallial sinus short or moderately 

 deep, but always rounded. Anterior left and posterior right dorsal 

 margins grooved to receive edge of opposite valve. Hinge-plate short 

 and rather small. Teeth, three in each valve, fairly strong, divergent, 

 and nearly equidistant. In right valve the posterior and median are 

 both bifid or grooved ; in the left only the median is bifid, but the 

 anterior is sometimes feebly grooved. The posterior left cardinal and 

 the right nymph bear fine linear riblets, and frequently all the teeth are 

 more or less rugose. The pedal scar is always separate from the anterior 

 adductor. 



Marcia, Adams, s.s. 



Type, Venus pinguis, (uhera. 



Shell oval or oblong, tumid, sometimes attenuated posteriorly, always 

 smooth with a vernicose periostracum. Lunule impressed, but convex 

 above the anterior teeth. Escutcheon depressed, but not defined. 

 Pallial sinus often extending to centre of valve. Teeth slender and 

 widely divergent ; the right median narrow, the left median thick, the 

 one grooved, the other bifid. 



Species. — M. pinguis, Chem. (including the vars. Ceylonensis, Sow., 

 triradiata, Chem., and nehulosa, Chem.) ; M. paupercula, Chem. (with 

 Ydixs. Kochi, Phil., amhigua, Desh,, and Kraussi, Desh.) ; ? Jf. inter- 

 rupta, Koch (Indian Ocean); M. fumigata, Sow. {= Icevigata, Sow.), 

 Australia. 



