25 



tendente divisa ; area antica striis concentricis et postice strlis radian- 

 tibiis ornata ; area postero-dorsali triangulari eburnea, sulco radiante 

 partita, et striis lamellosis concentricis insculpta. Long. 18; alt. 13 ; 

 lat. 10 millim. Inhabits the China Sea, lat. 24° N. ^Y. S. 



The cartilage pit is oblong, narrow, somewhat oblique, and nearly 

 appressed against the margin ; behind it is a protrusion of the margin 

 almost like a lateral tooth. Only one valve having been examined, 

 the generic place is not fully settled. 



Paxop^a fragilis. T. elliptica, tenuis, fragilis, livido-albida, 

 concentrice undulata ; umbonibus submedianis ; extremitate anticji 

 obtuse rotundata ; extrem. postica subtruncata ; cardine debili ; apo- 

 physi ligamentali brevi ; dente elongato ; margine dorsali ad basin 

 dentis fissurata. Long. 2 ; alt. 1,5; lat. 1 inch. Inhabits Hakodadi 

 Bay. W. S. 



Remarkable for its fragile structure and waved surface, like some 

 of the Thraciee, or Mactraceae, or still more like Pholadomya. 



Panop^a gexerosa. Several specimens were obtained at 

 Awatska Bay, Kamtschatka, which are probably this species ; but 

 the beaks are much more anterior, the posterior truncation is much 

 more oblique and in a different direction, and the gape is much less 

 than in the specimen originally described. They have also a double 

 structure, — an inner porcellanous layer, and a more earthy, some- 

 what crystalline coat, which extends beyond the first at the margin. 

 This latter crystalline or tessellated structure is very clearly exhibited, 

 and probably obtains in all the species. The variation in outline 

 from the original type was so great that I had named these specimens 

 P. sagrinata. 



CoRBULA VEXUSTA. T. parva, solida, albida (vel rosacea) ovato- 

 triangularis, admodum compressa, subaequivalvis, concentrice arata, 

 liris intercurrentibus rotundatis; umbonibus medianis antice excavatis ; 

 extremitate antica rotundata ; extrem. postica altiori et latiori, vix 

 truncata ; margine dorsali arcuata ; declivitate umbonali carinata. 

 Long. 10; alt. 7; lat. 4 millim. Inhabits Hakodadi Bay, in shelly 

 sand, 5-8 fathoms. W. S. 



Some smaller specimens are proportionally shorter, and have the 

 grooves much more distant, and if seen alone, would be considered a 

 different species. 



CoRBULA (Azara) rustica. T. parva, ovato-trigonalis, solida, 

 Isevis, epidermide tenui rufescente induta ; umbonibus submedianis 

 inconspicuis, erosis ; valvae majoris marginibus dorsalibus arcuatis, 

 declivibus ; extremitate antica rotundata ; extrem. postica obtuse 

 truncata ; valva altera graciliori, penitus inclusa ; declivitate umbonali 

 obtuse angulata ; cardine debili ; cavositate cretacea. Long. 15; alt. 

 9 ; lat. 5 millim. Inhabits Whampoa. W. S. 



Some of the specimens are much more triangular than others. 



